Processes for Production of 2-Bromo-2,2-Difluoroethanol and 2-(Alkylcarbonyloxy)-1, 1-Difluoroethanesulfonic Acid Salt

ABSTRACT

Disclosed is a process for producing 2-bromo-2,2-difluoroethanol, which comprises reducing a bromodifluoroacetic acid derivative represented by the formula [1] by using an ate hydride complex as a reducing agent. 2-Bromo-2,2-difluoroethanol thus produced can be used as the starting material to carry out the esterification step, the sulfination step and the oxidation step in this order, thereby producing a 2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt, wherein A represents a substituted or unsubstituted linear, branched or cyclic alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 15 carbon atoms, a heteroaryloxy group having 4 to 15 carbon atoms, or a halogen atom.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser.No. 12/678,223, filed Mar. 15, 2010, which is a national stageapplication of international patent application no. PCT/JP2008/066041,filed Sep. 5, 2008. Priority is claimed based on Japanese patentapplication no. 2007-241606, filed Sep. 18, 2007, and Japanese patentapplication no. 2008-172944, filed Jul. 2, 2008.

TECHNICAL FIELD

The present invention relates to a process for producing2-bromo-2,2-difluoroethanol useful as an intermediate of medicines oragrichemicals, or as a synthetic intermediate or raw material forfunctional materials such as fluorine-containing polymers. Moreover, thepresent invention relates to a process for producing fluorine-containingsulfonates useful as: an intermediate for producing a photoacidgenerator useful as a chemically amplified resist material suitable fora micro-processing technology, particularly photolithography, in theproduction steps of semiconductor devices and the like; or anintermediate for producing solid electrolytes used in fuel cells or thelike. Furthermore, the present invention relates to a process forproducing fluorine-containing onium sulfonic acid salts that function asthe photoacid generator.

BACKGROUND OF THE INVENTION

Hitherto, processes for producing 2-bromo-2,2-difluoroethanol, whichhave been known, had been very few. Patent Document 1 presents adescription about producing 2-bromo-2,2-difluoroethanol by reacting asilver salt of 2,2-difluoro-3-hydroxypropionic acid with bromine.

Additionally, solid polymer electrolytes used as electrolytes for fuelcells are being developed briskly in recent years. Most of these have afluorine-containing sulfonic acid derivative at its end. Non-PatentDocument 1 reports a solid polymer electrolyte formed by copolymerizingacrylate which has a fluorine-containing sulfonic acid lithium salt atits end.

Furthermore, in recent years, the trend toward micro-scale pattern rulehas been increasing with the trend toward large-scale integration andhigh-speed of LSI. The trend toward a shorter wavelength of the exposurelight source lies behind it. For example, it has become possible tomass-produce DRAM (dynamic random-access memory) of 64M-bit (processingdimension is 0.25 μm or less) by the wavelength shortening from mercurylamp i-line (365 nm) to KrF excimer laser (248 nm). Furthermore, inorder to realize the production of DRAM's having integration degrees of256M and 1G or greater, a lithography using ArF excimer laser (193 nm)has been used.

As a resist suitable for such exposure wavelength, “chemically amplifiedresist material” attracts much attention. This contains a radiosensitiveacid generator (hereinafter referred to as “photoacid generator”) whichgenerates an acid by radiation irradiation (hereinafter, referred to as“exposure”), and is a pattern-forming material that forms a pattern bymaking a difference in solubility in developing agent between theexposed portion and the unexposed portion through a reaction using theacid generated by the exposure as a catalyst.

Also concerning a photoacid generator used for such a chemicallyamplified resist material, studies have been made variously. It has beenknown that, in a case where a photoacid generator as has been used for aconventional chemically amplified resist material whose light source isKrF excimer laser light to generate alkane or arenesulfonic acid is usedas a component of the above-mentioned ArF-type chemically amplifiedresist material, the acid strength is not sufficient to cleave anacid-unstable group so as not to allow resolution entirely, or that thesensitivity is so low as to make it unsuitable for the deviceproduction.

Therefore, as the photoacid generator for the ArF-type chemicallyamplified resist material, those that generate perfluoroalkanesulfonicacid high in acid strength are commonly used; however, perfluorooctanesulfonate and derivatives thereof, which are known as PFOS abbreviatedby their initials, causes problems of stability (non-degradability)stemmed from a C—F bond and of biological concentration and accumulationstemmed from hydrophobicity or lipophilicity. Additionally,perfluoroalkanesulfonic acid having 5 or more carbon atoms andderivatives thereof also begin to cause the above problems.

In order to address the above problems regarding PFOS, there has beendeveloped, at all parts, partially fluorinated alkanesulfonic acidshaving a reduced degree of fluorine substitution. For instance,alkoxycarbonylfluoromethanesulfonic acid onium salts such astriphenylsulfonium methoxycarbonyldifluoromethane sulfonate (PatentDocument 2), (4-methylphenyl)diphenylsulfonylt-butoxycarbonyldifluoromethane sulfonate (Patent Document 3) andtriphenylsulfonium(adamant-1-ylmethyl)oxycarbonyldifluoromethanesulfonate (Patent Document 4) have been developed as the acid generator.

On the other hand, triphenylsulfonium1,1,3,3,3-pentafluoro-2-benzoyloxypropane-1-sulfonate, which is a kindof alkylcarbonyloxyalkanesulfonic acid onium salt and has an ester bondopposite to that of the above-mentionedalkoxycarbonyldifluoromethanesulfonic acid onium salt, and the like havebeen developed (Patent Document 5).

The present applicant has found2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid onium saltsrepresented by the formula [8] or [13], which has three less fluorineatoms than the acid generators presented by the Patent Documents so asto be considered to less affect the environment even though identicalwith alkylcarbonyloxyalkanesulfonic acid onium salt. Additionally, thepresent applicant found this substance to function as an acid generatorhaving a high acid strength with the minimum possible number of fluorineatom, and to be excellent in compatibility with solvents or resins so asto be useful as the acid generator for the resist material, and alreadyfiled patent applications (Japanese Patent Application No. 2007-143879and Japanese Patent Application No. 2007-143880).

By the way, as a process of synthesizing the above-mentionedalkoxycarbonyldifluoromethanesulfonic acid onium salt, a reaction pathas represented by the following equation [2] has been known.

More specifically, the path including: synthesizing3,3,4,4-tetrafluoro-[1,2]oxathietane 2,2-dioxide [iii] in the firstplace from tetrafluoroethylene [i] and sulfur trioxide [ii]; thereaftersynthesizing [v] by a ring-opening reaction of [iii] with the use ofalcohol (ROH), or passing 3,3,4,4-tetrafluoro-[1,2]oxathietane2,2-dioxide [iv] through ring-opening isomerization of [iii] and thenpassing esterification of [iv] with the use of alcohol (ROH);subsequently converting [v] into a sulfonate (a sodium salt of sulfonicacid) [vi] with the use of a basic metal salt (mainly sodium hydroxide);and thereafter conducting an onium-salt exchange with the use of anonium salt (Q⁺X⁻: Q is a monovalent onium cation and X is mainlyhalogen) such as a sulfonium salt, thereby obtaining the target acidgenerator, alkoxycarbonyldifluoroalkanesulfonic acid onium salt [vii](Patent Document 2 and Patent Document 6).

On the other hand, as a process of synthesizing an onium salt of1,1,3,3,3-pentafluoro-2-benzoyloxypropane-1-sulfonic acid discussed inPatent Document 5, a reaction path as represented by the followingequation [3] is disclosed.

However, hitherto known processes for producing a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt have been veryfew, so that hitherto known processes for producing2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonic acid onium salt havebeen very few.

-   Patent Document 1: U.S. Pat. No. 2,678,953-   Patent Document 2: Japanese Patent Application Publication No.    2004-117959-   Patent Document 3: Japanese Patent Application Publication No.    2002-214774-   Patent Document 4: Japanese Patent Application Publication No.    2004-4561-   Patent Document 5: Japanese Patent Application Publication No.    2007-145797-   Patent Document 6: U.S. Pat. No. 2,852,554-   Non-Patent Document 1: Solid State Ionics, 1999, Volume 123, pages    233-242

SUMMARY OF THE INVENTION

A process disclosed in Non-Patent Document 1 with relation to theprocess for producing 2-bromo-2,2-difluoroethanol is not clear aboutdetails such as experimental conditions and yield, so as to be uncertainhow useful the process is; however, the process uses an expensive silversalt as the starting material in any case, so that the industrializationthereof is expected to be difficult from the economical viewpoint. Inaddition to this, 2,2-difluoro-3-hydroxypropionic acid (the raw materialfor the silver salt) itself is not a compound of commercial-scaledistribution to be enormously hard to get at the reagent level, so thatthe industrialization is considered to be hard.

The conventional production process of 2-bromo-2,2-difluoroethanol isthus extremely difficult, and therefore the establishment of theindustrial production process efficient and performable for a long timeto come has been desired.

Furthermore, the process for producingalkoxycarbonyldifluoromethanesulfonic acid salt, as shown in theequation [2] uses 3,3,4,4-tetrafluoro-[1,2]oxathietane 2,2-dioxide [iii]formed from tetrafluoroethylene [i] and sulfur trioxide [ii] as the rawmaterial. Tetrafluoroethylene [i] is highly chemically reactive and hasthe danger of explosion, as commonly known, so as to be hard to handlein large quantity. Additionally, sulfur trioxide [ii] is an oxidizingagent so strong as to violently react with flammable substances,reducing substances and organic compounds, and therefore brings the loadof handling in large quantity. As discussed above, in this processreagents having difficulty in handling in large quantity are mixed, sothat an enough attention to safety is needed. This reaction is thus highin degree of industrial difficulty, which necessarily makes the obtained3,3,4,4-tetrafluoro-[1,2]oxathietane 2,2-dioxide [iii] very expensive.

In addition, there is a problem of hydrogen fluoride or fluoride saltproduced as a large quantity of by-product by the conversion reaction ofthe 3,3,4,4-tetrafluoro-[1,2]oxathietane 2,2-dioxide ([iv] or [v]). Afluorine ion liberated from hydrogen fluoride or fluoride salt corrodesand devitrifies a glass reactor. Additionally, not only hydrogenfluoride itself but also hydrogen fluoride (serving as a strong acid)generated by contact between fluoride salt and acid make metallicreactors such as iron and stainless steel unusable, so that usablematerials for the reactors are greatly limited.

Thus, there exist some disadvantages in producingalkoxycarbonyldifluoromethanesulfonic acid salt.

On the other hand, in Patent Document 5,1,1,1,3,3,3-hexafluoro-2-propanol [viii] having 6 fluorine atoms servesas the starting material to construct1,1,3,3,3-pentafluoro-2-benzoyloxypropane-1-sulfonic acid salt [xi] asrepresented by the above equation [3]. Upon this, the sulfonic acid saltis led to be an onium salt of1,1,3,3,3-pentafluoro-2-benzoyloxypropane-1-sulfonic acid [xii]. Thissynthesizing process is characterized by passing an enolate representedby [ix] as an intermediate active species. An enolate ion is, generally,a chemical species which is hard to exist stably. However, in thecompound of Patent Document 5 whose CF₃ group bonding to carbon of C═Cdouble bond has a strong electron-attracting property, the enolate isstabilized, with which the above reaction is allowed as a result.

Meanwhile, the substrate of the present invention whose moietycorresponding to this “CF₃ group” is “H” is therefore largely reduced inelectron withdrawal against a double bond moiety. As a result, anenolate ion corresponding thereto becomes unstable so as to make itdifficult to perform a reaction corresponding to the reaction of thePatent Document (as shown in the following equation).

In actual fact, there has never been known a process for obtaining2,2-difluoroethen-1-yl aliphatic acid carboxylate or aromaticcarboxylate by using 2,2,2-trifluoroethanol as the starting material.Furthermore, there has never been found a report of forming an enolatesalt [CF₂═CHOM (M=Li, K, Na)] serving as a precursor of these.

Concerning the production of alkylcarbonyloxyalkanesulfonic acid, aproduction process of 2-alkylcarbonyloxy-1,1-difluoroethanesufonic acidsalt having 2 fluorine atoms has never been known, though a productionprocess of compound having a high number of fluorine atoms such as1,1,3,3,3-pentafluoro-2-benzoyloxypropane-1-sulfonic acid salt has beenknown.

In summary of the above, the difluoroalkanesulfonic acid skeleton having2 fluorine atoms preferably serves as an alkanesulfonic acid salt havinga sufficient acid strength with a lower number of fluorine atom;however, the conventional process of producingalkoxycarbonyldifluoromethanesulfonic acid salt has disadvantages, inwhich particularly the process of producing2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt has never beenknown.

Consequently, the establishment of the industrial production processcapable of economically and readily producing the difluoroalkanesulfonicacid skeleton having 2 fluorine atoms has been desired.

In view of the above, an object of the present invention is: to providea process for economically and readily producing2-bromo-2,2-difluoroethanol useful as an intermediate of medicines oragrichemicals from a commercially available raw material, in the firstplace; and to provide a process for producing2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salts useful as thephotoacid generator used for the chemically amplified resist material,by using 2-bromo-2,2-difluoroethanol as the raw material.

The present inventors have eagerly made studies in order to achieve theabove object. The present invention includes [Embodiment 1] to[Embodiment 4] as will be discussed below.

Embodiment 1

To begin with, studies were made on a process of synthesizing2-bromo-2,2-difluoroethanol, a key compound common in all of the presentinvention.

In course thereof, it was invented before anything else to use anindustrially economical and readily available bromodifluoroacetic acidderivative such as bromodifluoroacetic acid ester andbromodifluoroacetic acid halide as the starting material. It is, asrepresented by the following equation [4], a process for selectivelyreducing only a carbonyl group in the skeleton of bromodifluoroaceticacid ester or bromodifluoroacetic acid halide, without reducing acarbon-bromine bond of a bromodifluoromethyl group (while preventingdebromination).

(In the above equation [4], A represents a substituted or unsubstitutedlinear, branched or cyclic alkoxy group having 1 to 20 carbon atoms, asubstituted or unsubstituted aryloxy group having 6 to 15 carbon atomsor a heteroaryloxy group having 4 to 15 carbon atoms, orhalogen(fluorine, chlorine, bromine, iodine).)

It is generally difficult to selectively reduce only a carbonyl group(while preventing debromination) in such a compound as to have bothbromodifluoromethyl group and carbonyl group.

The present inventors actually carried out a hydrogenation reaction withthe use of an activated carbon-carrying palladium catalyst, at the earlystage of the studies. Upon this, the obtained as a result was not thetarget 2-bromo-2,2-difluoroethanol but principally ethyl difluoroacetate(see the following equation [5] and Comparative Example 1).

Then, against the same raw material, an active zinc was used as anreducing agent. In this case also, the obtained as a result was not thetarget 2-bromo-2,2-difluoroethanol but principally ethyl difluoroacetate(see the following equation [6] and Comparative Example 2).

As a reducing agent capable of selectively reducing the carbonyl group,sodium borohydride (NaBH₄) which is a kind of ate hydride complexes iswidely known. For example, a report is disclosed by Journal of OrganicChemistry, 1991, Volume 56, pages 4322-4325, in which1,3-dibromo-1,1-difluoroalkanes are reduced in the use of sodiumborohydride (NaBH₄) thereby obtaining 1,1-difluoroalkanes. An example ofthe reaction discussed in the document is represented by the followingequation [7].

It has been known that sodium borohydride (NaBH₄) thus acts on thebromodifluoromethyl group thereby causing debromination reaction in areductive manner.

Furthermore, the present inventors reacted ethyl6-bromo-5,5,6,6-tetrafluorohexanoic acid having both bromodifluoromethylgroup and carbonyl group with sodium borohydride (NaBH₄). In this casealso, a compound whose bromodifluoromethyl group was debrominated in areductive manner (see the following equation [8] and Comparative Example3).

From the results of the above, it was expected to be difficult to usesodium borohydride (NaBH₄) for the selective reduction of carbonyl groupof the bromodifluoroacetic acid derivative no matter how excellentsodium borohydride is as a carbonyl-selective reducing agent.

However, the present inventors found that the target2-bromo-2,2-difluoroethanol could be specifically obtained at aselectivity of about 100% in spite of the above-mentioned expectationwhen conducting reduction on bromodifluoroacetic acid derivativerepresented by the formula [1] by using the ate hydride complex as thereducing agent

For example, when conducting reduction on bromodifluoroacetic acid esterby using sodium borohydride (NaBH₄) (an ate hydride complex) as thereducing agent, 2-bromo-2,2-difluoroethanol can be obtained at aselectivity of about 100%. The further surprising fact is that it hasbecome clear that 2-bromo-2,2-difluoroethanol is obtained at aselectivity of about 100% also in a case of using lithium aluminohydride(LiAlH₄) as well as the case of sodium borohydride (NaBH₄), the lithiumaluminohydride being a kind of ate hydride complexes and said to have areduction capability greater than that sodium borohydride has (see thefollowing equation [9] and Examples 1 and 2).

Moreover it has become clear, also concerning bromodifluoroacetic acidhalide, that 2-bromo-2,2-difluoroethanol can be obtained by using sodiumborohydride (NaBH₄) which is a kind of ate hydride complexes as thereducing agent (see Example 3).

The present inventors thus found a novel production process suitable fora large-scale production of 2-bromo-2,2-difluoroethanol useful as anorganic intermediate.

Furthermore, the present inventors have eagerly made studies onsynthesizing various kinds of2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salts by using2-bromo-2,2-difluoroethanol produced by the above-mentioned process asthe starting material ([Embodiment 2] to [Embodiment 4]).

Embodiment 2

The present inventors had reached a finding that2-bromo-2,2-difluoroethanol obtained by the process of [Embodiment 1](which is also referred to as “a 1st step”) as represented by theequation [9] is first of all introduced in order into reactions of 2ndto 4th steps thereby producing a2-alkylcarbonyloxy-1,1-dirluoroethanesulfonic acid salt represented bythe equation [2] (Equation [10]).

(In the above equation [10], A is synonymous with A represented in theequation [4]. R represents a substituted or unsubstituted linear,branched or cyclic alkyl group having 1 to 20 carbon atoms, asubstituted or unsubstituted aryl group having 6 to 15 carbon atoms or aheteroaryl group having 4 to 15 carbon atoms. However, those having inits structure an unconjugated unsaturated moiety (a double or triplebond) as R, other than aromatic rings having a conjugated unsaturatedmoiety, such as aryl group and heteroaryl group, are excepted. X′represents a hydroxyl group or a halogen. M⁺ represents a countercation.)

More specifically, it has been found that; 2-bromo-2,2-difluoroethanolis produced in the above-mentioned reduction step (a 1st step); then,the compound is reacted with acids or acid halides represented in theformula [3] or acid anhydrides represented in the formula [4] therebyobtaining a carboxylic acid bromodifluoroethyl ester represented by theformula [5] (a 2nd step; an esterification step 1); then, the carboxylicacid bromodifluoroethyl ester is reacted in the presence of asulfinating agent and a base so as to be converted into a2-alkylcarbonyloxy-1,1-difluoroethanesulfinic acid salt represented bythe formula [6] (a 3rd step: a sulfination step); and then the sulfinicacid salt is reacted with an oxidizing agent (a 4th step: an oxidationstep) thereby obtaining a 2-alkylcarbonyloxy-1,1-difluoroethanesulfonicacid salt represented by the formula [2].

In order to obtain a 2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acidsalt represented by the formula [2], it is critically important toconduct the above-mentioned step in order. As shown in the followingequation [11], there can be considered a process of carrying out a priorsulfination of 2-bromo-2,2-difluoroethanol, oxidation and thenesterification and a process of carrying out a prior sulfination of2-bromo-2,2-difluoroethanol, esterification and an oxidation in the end;however, the sulfination of 2-bromo-2,2-difluoroethanol is difficult tobe done and therefore the adoption thereof is found not to be allowed(Comparative Example 4).

(In the above equation [11], R and M⁺ are synonymous with R and M⁺represented in the equation [10].)

The present inventors thus found a novel production process suitable fora large-scale production of2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt useful as anintermediate for producing a photoacid generator for a chemicallyamplified resist material or as an intermediate for producing a solidpolymer electrolyte for fuel cells.

Embodiment 3

It has been found that the 2-alkylcarbonyloxy-1,1-dirluoroethanesulfonicacid salt represented by the equation [2] and synthesized by the processof [Embodiment 2] is introduced further into “an onium-salt exchangingstep (a 5th step)” thereby obtaining a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid onium saltrepresented by the formula [8] (see the following equation [12]).

(In the above equation [12], R and M⁺ are synonymous with R and M⁺represented in the equation [10]. X⁻ represents a monovalent anion. Q⁺represents a sulfonium cation represented by the following formula (a)or the following formula (b) or an iodonium cation represented by thefollowing formula (c).)

In the formula (a), R¹, R² and R³ mutually independently represent asubstituted or unsubstituted linear or branched alkyl group, alkenylgroup or oxoalkyl group having 1 to 10 carbon atoms, or a substituted orunsubstituted aryl group, aralkyl group or aryloxoalkyl group having 6to 18 carbon atoms. Furthermore, any two or more of R¹, R² and R³ maybond to each other to form a ring together with a sulfur atom shown inthe formula.

In the formula (b): R⁴ represents a substituted or unsubstituted linear,branched or cyclic alkyl group or alkenyl group having 1 to 20 carbonatoms or a substituted or unsubstituted aryl group having 6 to 14 carbonatoms; m represents an integer of from 1 to 5; and n represents 0 (zero)or 1.

In the formula (c): R⁴ represents a substituted or unsubstituted linear,branched or cyclic alkyl group or alkenyl group having 1 to 20 carbonatoms or a substituted or unsubstituted aryl group having 6 to 14 carbonatoms; q represents an integer of from 0 (zero) to 5; and n represents 0(zero) or 1.

Namely, by the process of [Embodiment 3] the synthesis of2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid onium salt useful asa photoacid generator used for a chemically amplified resist materialhas become possible.

Embodiment 4

As discussed above, R, a functional group of the compound synthesized in[Embodiment 3], is limited in kind. In other words, R, a functionalgroup of the compound synthesized in [Embodiment 3], is “a substitutedor unsubstituted linear, branched or cyclic alkyl group having 1 to 20carbon atoms, a substituted or unsubstituted aryl group having 6 to 15carbon atoms or a heteroaryl group having 4 to 15 carbon atoms”, fromwhich those having in its structure an unconjugated unsaturated moiety(a double or triple bond) as R, other than aromatic rings having aconjugated unsaturated moiety, such as aryl group and heteroaryl group,are excepted. This is derived from the 3rd step (the sulfination step).The present inventors has found it difficult to obtain the targetsulfinated compound when using a compound having in its structure anunconjugated unsaturated moiety (a double or triple bond) as R as theraw material for the 3rd step (the sulfination step) because of a sidereaction caused at the unconjugated unsaturated moiety.

Examples of R having an unconjugated unsaturated moiety (a double ortriple bond) are linear, branched or cyclic alkenyl groups. Concreteexamples of the alkenyl groups include vinyl group, allyl group,1-methylethenyl group, 1-methylallyl group, 2-methylallyl group,1-propenyl group, isopropenyl group, 2-butenyl group, 3-butenyl group,1,3-butadienyl group, 2-pentenyl group, 4-pentenyl group, 2-hexenylgroup, 5-hexenyl group, cyclopropenyl group, cyclopentenyl group,cyclohexenyl group and 5-norbornen-1-yl group (the following equation[13] and the equation [14]; Comparative Examples [5] and ComparativeExamples [6]).

In view of the above circumstances, the present inventors found a novelsynthesis route in which a 2-alkylcarbonyloxy-1,1-difluoroethanesulfonicacid salt represented by the formula [2] and obtained in the above[Embodiment 2] is used as the starting material, and additionallyreached the finding that the above problems are solved by taking thisroute.

More specifically, it has been found that a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid onium salt useful asa photoacid generator for a resist material and represented by theformula [13]

is obtained: by conducting saponification reaction (hydrolysis reactionin the presence of a basic substance) on the2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt represented bythe formula [2] and obtained by the above [Embodiment 2] (a 5′th step: asaponification step) thereby obtaining a2-hydroxy-1,1-difluoroethanesulfonic acid salt represented by theformula [9]

then by reacting it with a carboxylic acid derivative represented by theformula [10]

or the formula [11]

(a 6th step: an esterification step 2) thereby obtaining a2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonic acid salt represented bythe formula [12]

and then by conducting an onium-salt exchange thereon (a 7th step: anonium-salt exchanging step 2) by using a monovalent onium saltrepresented by the formula [7]

[Chemical formula 22]

Q⁺X⁻  [7]

(see the following equation [15]).

(In the above equation [15], M⁺ shown in the formula [9] and the formula[12] represents a counter cation. X′ of the formula [10] is synonymouswith X′ of the formula [3]. In the formula [10] to the formula [13], R′represents a substituted or unsubstituted linear, branched or cyclicalkyl group having 1 to 20 carbon atoms, a substituted or unsubstitutedlinear, branched or cyclic alkenyl group having 1 to 20 carbon atoms, asubstituted or unsubstituted aryl group having 6 to 15 carbon atoms or aheteroaryl group having 4 to 15 carbon atoms.)

In this finding, the important point is that R′, a substituent for the2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid onium saltrepresented by the formula [13], includes “those having in its structurean unconjugated unsaturated moiety (a double or triple bond)”. Namely,this [Embodiment 5] is useful particularly for a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid onium salt having inits structure an unconjugated unsaturated moiety as a substituent R′,among those useful as the photoacid generator for the chemicallyamplified resist material.

Particularly, those having an unconjugated unsaturated moiety at the endof the substituent, i.e.2-(ω-alkenylcarbonyloxy)-1,1-difluoroethenesulfonic acid onium salts,can be fixed in a resist resin by being copolymerized with other monomerand therefore can be used as “a photoacid generator of a type carried bythe resist resin”, as well as a polymerizable and fluorine-containingsulfonic acid onium salt disclosed in International Patent ApplicationPublication No. 2006/121096 A1. The “photoacid generator of the typecarried by the resist resin” is a new type of photoacid generator whohas recently been receiving attention because of its high performancessuch as a high resolution. In such a sense also,2-(ω-alkenylcarbonyloxy)-1,1-difluoroethenesulfonic acid onium saltshaving an unconjugated unsaturated moiety at the end of its substituentare extremely useful.

As discussed above, [Embodiment 1] to [Embodiment 4] are suitablyselected thereby allowing to produce compounds of wide kinds ofsubstituents, such as: 2-bromo-2,2-difluoroethanol useful as anintermediate of medicines or agrichemicals;2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salts useful as anintermediate for a photoacid generator for a resist material or as anintermediate for an electrolyte for a fuel cell; and2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid onium salts useful asa photoacid generator. The present invention has thus been completed.

Moreover, the present inventors have found novel compounds(triphenylsulfonium 1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonateand sodium 2-hydroxy-1,1-difluoroethanesulfonate) in the course ofstudying these reaction steps.

The present invention, in which all necessary raw materials areinexpensive and the operation in any of the steps is so convenience asto be able to perform with a less operational burden, is much moreadvantageous than the conventional means in terms of an industrial-scaleproduction of the target 2-bromo-2,2-difluoroethanol or the target2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salts.

According to the present invention, there is provided a process forproducing 2-bromo-2,2-difluoroethanol (a first process) which processcomprises a step of reducing a bromodifluoroacetic acid derivativerepresented by the formula [1] by using an ate hydride complex as areducing agent.

(In the above formula [1], A represents a substituted or unsubstitutedlinear, branched or cyclic alkoxy group having 1 to 20 carbon atoms, asubstituted or unsubstituted aryloxy group having 6 to 15 carbon atomsor heteroaryloxy group having 4 to 15 carbon atoms, or halogen.)

Furthermore, according to the present invention, there is provided aprocess for producing a 2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonicacid salt represented by the formula [2] (a second process)

which process comprises the following four steps: a 1st step (areduction step) of reducing a bromodifluoroacetic acid derivativerepresented by the formula [1]

by using an ate hydride complex as a reducing agent, thereby producing2-bromo-2,2-difluoroethanol; a 2nd step (an esterification step 1) ofreacting the 2-bromo-2,2-difluoroethanol obtained by the 1st step (thereduction step) with a carboxylic acid derivative represented by theformula [3]

or the formula [4]

thereby obtaining a carboxylic acid bromodifluoroethyl ester representedby the formula [5]

a 3rd step (a sulfination step) of reacting the carboxylic acidbromodifluoroethyl ester represented by the formula [5] and obtained bythe 2nd step (the esterification step 1) with a base in the presence ofa sulfinating agent, thereby obtaining a2-(alkylcarbonyloxy)-1,1-difluoroethanesulfinic acid salt represented bythe formula [6]

a 4th step (an oxidation step) of reacting the2-(alkylcarbonyloxy)-1,1-difluoroethanesulfinic acid salt represented bythe formula [6] and obtained by the 3rd step (the sulfination step) withan oxidizing agent thereby obtaining a2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonic acid salt represented bythe formula [2].

(In the above formula [1], A represents a substituted or unsubstitutedlinear, branched or cyclic alkoxy group having 1 to 20 carbon atoms, asubstituted or unsubstituted aryloxy group having 6 to 15 carbon atomsor heteroaryloxy group having 4 to 15 carbon atoms, or halogen. In theformula [2] to the formula [6], R represent a substituted orunsubstituted linear, branched or cyclic alkyl group having 1 to 20carbon atoms, a substituted or unsubstituted aryl group having 6 to 15carbon atoms or heteroaryl group having 4 to 15 carbon atoms; however,those having in its structure an unconjugated unsaturated moiety (adouble or triple bond) as R are excepted. In the formula [3], X′represents hydroxyl group or halogen. In the formula [2] or the formula[6], M⁺ represents a counter cation.)

Furthermore, according to the present invention, there is provided aprocess for producing a 2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonicacid onium salt represented by the formula [8] (a third process)

comprising: a step of conducting an onium-salt exchange (a 5th step: anonium-salt exchanging step 1) on the2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonic acid salt represented bythe formula [2] and obtained by the process as claimed in Claim 2, byusing a monovalent onium salt represented by the formula [7].

[Chemical formula 32]

Q⁺X⁻  [7]

(In the formula [7], X⁻ represents a monovalent anion. In the formula[8], R is synonymous with R of the formula [2] to the formula [6]. Inthe formula [7] and the formula [8], Q⁺ represents a sulfonium cationrepresented by the following formula (a) or the following formula (b),or an iodonium cation represented by the following formula (c).

In the formula (a), R¹, R² and R³ mutually independently represent asubstituted or unsubstituted linear or branched alkyl group, alkenylgroup or oxoalkyl group having 1 to 10 carbon atoms, or a substituted orunsubstituted aryl group, aralkyl group or aryloxoalkyl group having 6to 18 carbon atoms. Furthermore, any two or more of R¹, R² and R³ maybond to each other to form a ring together with a sulfur atom shown inthis formula.

In the formula (b), R⁴ represents a substituted or unsubstituted linear,branched or cyclic alkyl group or alkenyl group having 1 to 20 carbonatoms or a substituted or unsubstituted aryl group having 6 to 14 carbonatoms. m represents an integer of from 1 to 5, and n represents 0 (zero)or 1.

In the formula (c), R⁴ represents a substituted or unsubstituted linear,branched or cyclic alkyl group or alkenyl group having 1 to 20 carbonatoms or a substituted or unsubstituted aryl group having 6 to 14 carbonatoms. q represents an integer of from 0 (zero) to 5, and n represents 0(zero) or 1.

Furthermore, according to the present invention, there is provided aprocess for producing a 2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonicacid onium salt represented by the formula [13] (a fourth step)

comprising: a step (a 5′th step: a saponification step) of saponifyingthe 2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonic acid saltrepresented by the formula [2] and obtained by the process as claimed inClaim 2 thereby obtaining a 2-hydroxy-1,1-difluoroethanesulfonic acidsalt represented by the formula [9]

a step (a 6th step: an esterification step 2) of reacting the2-hydroxy-1,1-difluoroethanesulfonic acid salt with a carboxylic acidderivative represented by the formula [10]

or the formula [11]

thereby obtaining a 2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonic acidsalt represented by the formula [12]

and a step of conducting an onium-salt exchange on the2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonic acid salt by using amonovalent onium salt represented by the formula [7].

[Chemical formula 41]

Q⁺X⁻  [7].

(In the formula [9] and the formula [12], M⁺ represents a countercation. In the formula [10], X′ is synonymous with X′ of the formula[3]. In the formula [10] to the formula [13], R′ represents asubstituted or unsubstituted linear, branched or cyclic alkyl grouphaving 1 to 20 carbon atoms, a substituted or unsubstituted linear,branched or cyclic alkenyl group having 1 to 20 carbon atoms, asubstituted or unsubstituted aryl group having 6 to 15 carbon atoms orheteroaryl group having 4 to 15 carbon atoms. In the formula [13], Q issynonymous with Q of the formula [7] and the formula [8].)

In the reduction step of the first or second process, the ate hydridecomplex used as the reducing agent may be a hydride complex based onboron hydride or aluminum hydride.

Furthermore in the reduction step of the first or second process, theate hydride complex used as the reducing agent is sodium borohydride orlithium aluminohydride.

Furthermore, in the reduction step of the first or second process, thebromodifluoroacetic acid derivative may be a bromodifluoroacetic acidderivative represented by the formula [14].

(In the formula [14], R″ represents a substituted or unsubstitutedlinear, branched or cyclic alkyl group having 1 to 6 carbon atoms.)

Furthermore, according to the present invention, there is providedtriphenylsulfonium 1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonatewhich is a novel compound corresponding to the2-(alkylcarbonyloxy)-1,1-difluoroethanesulfonic acid onium saltrepresented by the formula [13].

Furthermore, according to the present invention, there is providedsodium 2-hydroxy-1,1-difluoroethanesulfonate which is a novel compoundcorresponding to the 2-hydroxy-1,1-difluoroethanesulfonic acid saltrepresented by the formula [9].

DETAILED DESCRIPTION

According to the present invention, 2-bromo-2,2-difluoroethanol (usefulas an intermediate of medicines or agrichemicals or as a syntheticintermediate or raw material for functional materials such asfluorine-containing polymers and the like) can be produced from abromodifluoroacetic acid derivative available at low cost, in only oneconvenient process step at a high yield and on an industrial scale,which is an effect of the present invention. Additionally,fluorine-containing sulfonic acid salts (useful as an intermediate forproducing a solid electrolyte used for a fuel cell or the like or anintermediate for producing a photoacid generator useful as a chemicallyamplified resist material suitable for micromachining techniques (e.g.photolithography in particular) applied in industrial processes of asemiconductor device or the like) can be produced conveniently at a highyield and at an industrial scale by using 2-bromo-2,2-difluoroethanol asa raw material, which is a further effect of the present invention.Moreover, fluorine-containing sulfonic acid onium salts that function asthe photoacid generator can be produced conveniently at a high yield andat an industrial scale, which is a still further effect of the presentinvention.

Hereinafter, the present invention will be discussed in more detail. Thepresent invention includes, as represented by the following equation[16],

five steps comprising: a step of reducing a bromodifluoroacetic acidderivative represented by the formula [1] by using an ate hydridecomplex as a reducing agent, thereby producing2-bromo-2,2-difluoroethanol (an objective of the embodiment 1 of thepresent invention) (a 1st step; a reduction step); a step of esterifyingthe thus obtained 2-bromo-2,2-difluoroethanol thereby obtaining acarboxylic acid bromodifluoroethyl ester represented by the formula [5](a 2nd step: an esterification step); a step of reacting the thusobtained carboxylic acid bromodifluoroethyl ester represented by theformula [5] in the presence of a sulfinating agent thereby obtaining a2-alkylcarbonyloxy-1,1-difluoroethanesulfinic acid salt represented bythe formula [6] (a 3rd step: a sulfination step); a step of reacting thethus obtained 2-alkylcarbonyloxy-1,1-difluoroethanesulfinic acid saltrepresented by the formula [6] with an oxidizing agent thereby obtaininga 2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt (an objectiveof the embodiment 2 of the present invention) represented by the formula[2] (a 4th step: an oxidation step); and a step of carrying out anonium-salt exchange on the thus obtained2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt represented bythe formula [2] by using a monovalent onium salt represented by theformula [7], thereby obtaining a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid onium salt (anobjective of the embodiment 3 of the present invention) represented bythe formula [8] (a 5th step: an onium-salt exchanging step 1). Uponundergoing these steps, a 2-alkylcarbonyloxy-1,1-difluoroethanesulfonicacid onium salt not having an unconjugated unsaturated moiety (a doubleor triple bond) as R of the formula [8] can be obtained.

Those having the unconjugated unsaturated moiety (the double or triplebond) can be obtained by undergoing three steps comprising: a step ofsaponifying the 2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid saltrepresented by the formula [2] thereby obtaining a2-hydroxy-1,1-difluoroethanesulfonic acid salt represented by theformula [9] (a 5′th step: a saponification step); a step of esterifyingthe thus obtained 2-hydroxy-1,1-difluoroethanesulfonic acid saltrepresented by the formula [9] thereby producing a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt represented bythe formula [12] (a 6th step: an esterification step 2); and a step ofcarrying out a further onium-salt exchange by using a monovalent oniumsalt represented by the formula [7] (a 7th step: an onium-saltexchanging step 2). In such a manner that a bromodifluoroacetic acidderivative represented by the formula [1] undergoes the seven steps, a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid onium salt having anunconjugated unsaturated moiety (a double or triple bond) as R of theformula [13] also can be obtained.

Hereinafter, each of the steps will be discussed in detail. To beginwith, the 1st step of the present invention will be discussed. The 1ststep is a step of reducing a bromodifluoroacetic acid derivativerepresented by the formula [1] by using an ate hydride complex as areducing agent thereby producing 2-bromo-2,2-difluoroethanol (areduction step).

Bromodifluoroacetic acid derivative represented by the formula [1],which is the starting material of the present invention, isbromodifluoroacetic acid ester or bromodifluoroacetic acid halide.Concrete examples of bromodifluoroacetic acid ester are methylbromodifluoroacetate, ethyl bromodifluoroacetate, n-propylbromodifluoroacetate, i-propyl bromodifluoroacetate, n-butylbromodifluoroacetate, s-butyl bromodifluoroacetate, i-butylbromodifluoroacetate, t-butyl bromodifluoroacetate, n-pentylbromodifluoroacetate, n-hexyl bromodifluoroacetate, cyclohexylbromodifluoroacetate, phenyl bromodifluoroacetate, and benzylbromodifluoroacetate. Examples of bromodifluoroacetic acid halideinclude fluoride bromodifluoroacetate, chloride bromodifluoroacetate,bromide bromodifluoroacetate and iodide bromodifluoroacetate. Amongthese, the preferable in view of availability are methylbromodifluoroacetate, ethyl bromodifluoroacetate, n-propylbromodifluoroacetate, i-propyl bromodifluoroacetate, fluoridebromodifluoroacetate, chloride bromodifluoroacetate and bromidebromodifluoroacetate. The more preferable are ethylbromodifluoroacetate, fluoride bromodifluoroacetate and chloridebromodifluoroacetate. If taking handiness (volatility and a bad smell ofacid halide) into account, the most preferable is ethylbromodifluoroacetate.

The ate hydride complex used as a reducing agent in the 1st stepincludes boron hydrides such as sodium borohydride (NaBH₄), lithiumborohydride (LiBH₄), sodium cyanoborohydride (NaBH₃CN), zinc borohydride(Zn(BH₄)₂), potassium tri-sec-butylborohydride (K-selectride), andlithium tri-sec-butylborohydride (L-selectride), which have beencommonly used. Also included are aluminum hydrides such as lithiumaluminohydride (LiAlH₄), lithium tri-sec-butoxyaluminohydride(LiAlH(Ot-C₄H₉)₃), lithium trimethoxyaluminohydride (LiAlH(OCH₃)₃),diisobutylaluminum hydride ((i-C₄H₉)₂AlH) and sodiumbis(methoxyethoxy)aluminumhydride (NaAlH₂(OCH₂CH₂OCH₃)₂), which havebeen commonly used. Among these, the preferable in views of economy,handiness and availability are sodium borohydride (NaBH₄), lithiumaluminohydride (LiAlH₄), lithium tri-sec-butoxyaluminohydride(LiAlH(Ot-C₄H₉)₃), diisobutylaluminum hydride ((i-C₄H₉)₂AlH) and sodiumbis(methoxyethoxy)aluminumhydride (NaAlH₂(OCH₂CH₂OCH₃)₂). Theparticularly preferable are sodium borohydride (NaBH₄) and lithiumaluminohydride (LiAlH₄).

An amount of the reducing agent to be used, relative to 1 mole ofbromodifluoroacetic acid derivative, is preferably not less than thenumber of moles determined by the following [Equation 1].

The required number of moles of the reducing agent=2/the number ofactive hydrogen atoms included in a molecule of the reducing agent  [Equation 1]

More specifically, the required number of moles is not less than 0.5mole in the cases of sodium borohydride (NaBH₄) and of lithiumaluminohydride (LiAlH₄); not less than 2.0 moles in the cases of lithiumtri-sec-butoxyaluminohydride (LiAlH(Ot-C₄H₉)₃) and of diisobutylaluminumhydride ((i-C₄H₉)₂AlH); and not less than 1.0 mole in the case of sodiumbis(methoxyethoxy)aluminumhydride (NaAlH₂(OCH₂CH₂OCH₃)₂). A used amountof these reducing agents is preferably 1 to 3 times the required numberof moles, though normally 0.8 to 5 times the required number of moles. Aused amount of exceeding the above range is surely allowed, but notpreferable since it may cause a side reaction (such as reduction of acarbon-bromine bond of bromodifluoromethyl group), depending on theconditions.

These reducing agents may be used singly or in combination of not lessthan two kinds of these in a coexistent manner. However, coexistence ofother than the above-mentioned ate hydride complexes is not preferable.Particularly, reducing agents that have hitherto been reported to reducethe bromine-carbon bond thereby causing debromination are notpreferable. Concrete examples thereof are active zinc and metallicsodium. Additionally, sodium hydride (NaH) and lithium hydride (LiH),both of which are hydride type reducing agents but do not apply to the“ate” hydride complex, are also not preferable since these areexcessively strong as a reducing agent. It is particularly preferablenot to allow the coexistence of the reducing agents which do not applyto the “ate hydride complex” in the system at all. In the event thatthese coexist in the form of impurities, the amount thereof ispreferably less than 0.1 mole and particularly preferably less than 0.05mole relative to 1 mole of the above-mentioned “ate hydride complex”.

In this step, a normal solvent is used. Examples of the solvent include:water; DMF; N,N-dimethyl sulfoxide (DMSO); alcohols such as methanol,ethanol and 2-propanol; ethers such as diethyl ether, tetrahydrofuran,dioxane, butyl methyl ether and diisopropyl ether; alkanes such asn-pentane, n-hexane, n-heptane and n-octane; and aromatic compounds suchas benzene, toluene and xylene; however, the examples are not limited tothese. Moreover, these solvents may be used singly or in combination ofnot less than two kinds thereof.

The preferably used solvent differs according to the used reducing agentand reaction substrate. For example, in the case of using sodiumborohydride (NaBH₄), water may be used if the reaction substrate iswater-soluble. If the reaction substrate is not water-soluble, however,alcohols such as methanol, ethanol and 2-propanol and ethers such asdiethyl ether, tetrahydrofuran, dioxane, butyl methyl ether anddiisopropyl ether are preferable, and additionally methanol,tetrahydrofuran and diisopropyl ether are particularly preferable. Inthe case of using lithium aluminohydride (LiAlH₄) alcohols are notpreferable while ethers such as diethyl ether, tetrahydrofuran, dioxane,butyl methyl ether and diisopropyl ether are preferable. Among these,tetrahydrofuran and diisopropyl ether are particularly preferable.

The reaction can be conducted in air, but preferably conducted in aninert gas such as nitrogen and argon. In this step, the reactiontemperature ranges normally from −100 to 200° C., preferably from −78 to100° C., and more preferably from 0 to 70° C. Furthermore, the reactiontime ranges about from 5 minutes to 24 hours; however, it is preferablethat a temporal point at which the raw material bromodifluoroacetic acidderivative is consumed is determined, by analytical devices such as gaschromatography (GC) and nuclear magnetic resonance (NMR), as theendpoint of the reaction.

Upon termination of the reaction, 2-bromo-2,2-difluoroethanol can beobtained by normal means including extraction, distillation and thelike. Moreover, it can be purified by column chromatography, precisedistillation or the like, as necessary.

Then the 2nd step of the present invention will be discussed. The 2ndstep is a step of reacting the obtained 2-bromo-2,2-difluoroethanol witha carboxylic acid derivative represented by the formula [3] or theformula [4] to cause esterification thereby obtaining a carboxylic acidbromodifluoroethyl ester represented by the formula [5] (theesterification step 1).

In the formula [3] or the formula [4], R represents a substituted orunsubstituted linear, branched or cyclic alkyl group having 1 to 20carbon atoms, a substituted or unsubstituted aryl group having 6 to 15carbon atoms or heteroaryl group having 4 to 15 carbon atoms. However,those having in its structure an unconjugated unsaturated moiety (adouble or triple bond) as R are excepted. Additionally, X′ as shown inthe formula [3] represents hydroxyl group or halogen (fluorine,chlorine, bromine or iodine).

Concrete examples of R as shown in the formula [3] or the formula [4]are methyl group, ethyl group, n-propyl group, isopropyl group,cyclopropyl group, n-butyl group, sec-butyl group, isobutyl group,tert-butyl group, n-pentyl group, cyclopentyl group, n-hexyl group,2-ethylhexyl group, cyclohexyl group, n-octyl group, n-decyl group,n-dodecyl group, 1-adamantyl group, 2-adamantyl group,bicyclo[2.2.1]hepten-2-yl group, 1-adamantanemethyl group,2-adamantanemethyl group, phenyl group, 4-methoxyphenyl group,4-tert-butylphenyl group, 4-biphenyl group, 1-naphthyl group, 2-naphthylgroup, 10-anthranyl group and 2-furanyl group. Examples of R includingcarbonyl group, lactone and hydroxyl group are as follows:

(Each dotted line represents a bonding moiety.)

A concrete process for producing carboxylic acid bromodifluoroethylester represented by the formula [5] by reacting2-bromo-2,2-difluoroethanol obtained in the 1st step with carboxylicacids and carboxylic acid halides represented by the formula [3] orcarboxylic acid anhydrides represented by the formula [4] is notparticularly limited and therefore adopted from any of commonly knownesterification processes.

Examples of the esterification processes are: a process of dehydratingcondensation of a carboxylic acid represented by the formula [3] (X′═OH)and 2-bromo-2,2-difluoroethanol in the presence of an acid catalyst(Fischer esterification); and a process of reacting2-bromo-2,2-difluoroethanol obtained in the 1st step with carboxylicacid halides (X′═Cl, Br, I, F) represented by the formula [3] orcarboxylic acid anhydrides represented by the formula [4].

When using a carboxylic acid represented by the formula [3] (X′═OH), thecarboxylic acid which is to act on 2-bromo-2,2-difluoroethanol andrepresented by the formula [3] is used normally in an amount rangingfrom 0.1 to 5 moles, preferably from 0.2 to 3 moles and more preferablyfrom 0.5 to 2 moles relative to 1 mole of 2-bromo-2,2-difluoroethanol.It is particularly preferable to use the carboxylic acid in an amountwithin a range of from 0.8 to 1.5 moles.

Normally in the reaction, an aprotic solvent such as dichloroethane,toluene, ethylbenzene, monochlorobenzene, acetonitrile andN,N-dimethylformamide is used. These solvents may be used singly or incombination of not less than two kinds thereof.

The reaction temperature is normally within a range of from 0 to 200°C., preferably from 20 to 180° C., and more preferably from 50 to 150°C. It is preferable to conduct the reaction while stirring.

The reaction time depends on the reaction temperature; however, itranges normally from several minutes to 100 hours, preferably from 30minutes to 50 hours and more preferably from 1 to 20 hours. It ispreferable that a temporal point at which the raw material2-bromo-2,2-difluoroethanol is consumed is determined, by analyticaldevices such as gas chromatography (GC) and nuclear magnetic resonance(NMR), as the endpoint of the reaction.

Normally, this reaction is conducted with the addition of an organicacid such as para-toluenesulfonic acid and/or an inorganic acid such assulfuric acid, as an acid catalyst. Moreover, 1,1′-carbonyldiimidazole,N,N′-dicyclohexylcarbodiimide or the like may be added as a dehydratingagent. An amount of the acid catalyst to be used is not particularlylimited but preferably within a range of from 0.0001 to 10 moles,preferably from 0.001 to 5 moles and more preferably from 0.01 to 1.5mole relative to 1 mole of 2-bromo-2,2-difluoroethanol.

When esterification reaction using the acid catalyst is conducted whilecarrying out dehydration, for example, by using Dean-Stark apparatus,the reaction time tends to be shortened, which is preferable.

Upon termination of the reaction, carboxylic acid bromodifluoroethylester represented by the formula [5] can be obtained by normal meansincluding extraction, distillation, recrystallization and the like.Moreover, it can be purified by column chromatography, recrystallizationor the like, as necessary.

On the other hand, in the case of using carboxylic acid halidesrepresented by the formula [3] or carboxylic acid anhydrides representedby the formula [4], a used amount of the carboxylic acid halidesrepresented by the formula [3] or the carboxylic acid anhydridesrepresented by the formula [4] is not particularly limited; however, itranges normally from 0.1 to 5 moles, preferably from 0.2 to 3 moles andmore preferably from 0.5 to 2 moles relative to 1 mole of2-bromo-2,2-difluoroethanol. It is particularly preferable to use thecarboxylic acid halides or the carboxylic acid anhydrides in an amountranging from 0.8 to 1.5 moles.

The reaction may be conducted in the absence of solvents or may beconducted in a non-reactive solvent. Such solvents are required only tobe non-reactive and not particularly limited. Hence the reaction may beconducted in, for example, water, an organic solvent, or a mixture ofthese. Examples of the organic solvent include: hydrocarbon-basedsolvents such as n-hexane, benzene and toluene; ketone-based solventssuch as acetone, methyl ethyl ketone and methyl isobutyl ketone;ester-based solvents such as ethyl acetate and butyl acetate;ether-based solvents such as diethyl ether, diethylene glycol dimethylether, tetrahydrofuran and dioxane; halogen-based solvents such asdichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane,tetrachloroethylene, chlorobenzene and ortho-chlorobenzene; and polarsolvents such as acetonitrile, N,N-dimethylformamide,N,N-dimethylimidazolidinone, dimethyl sulfoxide and sulfolane. Thesesolvents may be used singly or in combination of not less than two kindsthereof.

The reaction temperature is not particularly limited and normally withina range of from −78 to 150° C., preferably from −20 to 120° C. and morepreferably from 0 to 100° C.

The reaction time depends on the reaction temperature; however, itranges normally from several minutes to 100 hours, preferably from 30minutes to 50 hours and more preferably from 1 to 20 hours. It ispreferable that a temporal point at which the raw material2-bromo-2,2-difluoroethanol is consumed is determined, by analyticaldevices such as gas chromatography (GC) and nuclear magnetic resonance(NMR), as the endpoint of the reaction.

In the case of using carboxylic acid halides represented by the formula[3], the reaction may be conducted in the absence of catalyst whileremoving hydrogen halides (e.g. hydrogen chloride) being produced asby-product from the reaction system or may be conducted with the use ofa dehydrohalogenating agent (or an acid acceptor). Additionally, in thecase of using carboxylic acid anhydrides represented by the formula [4],the reaction may be conducted with the use of an acid acceptor forreceiving by-product acids.

Examples of the acid acceptor include: organic bases such astriethylamine, pyridine, picoline, dimethylaniline, diethylaniline,1,4-diazabicyclo[2.2.2]octane (DABCO) and1,8-diazabicyclo[5.4.0]undec-7-ene (DBU); and inorganic bases such assodium hydrogencarbonate, sodium carbonate, potassium carbonate, lithiumcarbonate, sodium hydroxide, potassium hydroxide, calcium hydroxide andmagnesium oxide. An amount of the acid acceptor to be used is notparticularly limited but ranges from 0.05 to 10 moles, preferably from0.1 to 5 moles and more preferably from 0.5 to 3 moles relative to 1mole of 2-bromo-2,2-difluoroethanol.

Upon termination of the reaction, carboxylic acid bromodifluoroethylester represented by the formula [5] can be obtained by normal meansincluding extraction, distillation, recrystallization and the like.Moreover, it can be purified by column chromatography, recrystallizationor the like, as necessary.

Then, the 3rd step of the present invention will be now discussed. The3rd step is a step of reacting carboxylic acid bromodifluoroethyl esterrepresented by the formula [5] and obtained in the 2nd step in thepresence of a sulfinating agent thereby obtaining a2-alkylcarbonyloxy-1,1-difluoroethanesulfinic acid salt (a sulfinationstep).

The sulfinating agent that can be used in the present invention isrepresented by the formula [15].

[Chemical Formula 46]

(S¹)_(m)(M¹)_(n)·pH_(2.)O   [15]

(in the above equation [15]: S¹ represents S₂O₄, HOCH₂SO₂, SO₄ or HSO₄;m and n represent an integer; p represents 0 (zero) or an integer; andM¹ represents Li, Na, K or NH₄.)

Concrete examples thereof are lithium dithionite, sodium dithionite,potassium dithionite, ammonium dithionite, lithiumhydroxymethanesulfinate, sodium hydroxymethanesulfinate, lithiumhydroxymethanesulfinate, potassium hydroxymethanesulfinate, ammoniumhydroxymethanesulfinate, lithium sulfite, sodium sulfite, potassiumsulfite, ammonium sulfite, lithium hydrogen sulfite sodium hydrogensulfite, potassium hydrogen sulfite and ammonium hydrogen sulfite. Amongthese, sodium dithionite and potassium dithionite are preferable, andsodium dithionite is particularly preferable.

The molar ratio of the sulfinating agent to carboxylic acidbromodifluoroethyl ester [5] is normally from 0.5 to 10, preferably from0.9 to 5.0 and particularly preferably 1.0 to 2.0.

Though this reaction can be conducted in air, the sulfinating agent issometimes decomposed by water content in air. It is, therefore,preferable to conduct the reaction in an atmosphere of nitrogen orargon.

The reaction is accelerated with the addition of base, though sometimesdeveloped without base. Therefore base is usually added thereto.Examples of the base to be added are lithium carbonate, sodiumcarbonate, potassium carbonate, lithium hydrogen carbonate, sodiumhydrogencarbonate and potassium hydrogencarbonate, and preferably sodiumhydrogencarbonate and potassium hydrogencarbonate.

This reaction is preferably conducted in a mixture solution of anorganic solvent and water. Examples of the organic solvent are loweralcohols, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide,acetonitrile and dimethyl sulfoxide, and particularly preferablyacetonitrile.

The ratio of the used organic solvent to 100 parts by weight of total ofthe organic solvent and water is normally not less than 5 parts byweight, preferably not less than 10 parts by weight, and more preferablywithin a range of from 20 to 90 parts by weight.

The reaction temperature is normally from 40 to 200° C., preferably from60 to 100° C. The reaction time is normally from 0.5 to 120 hours,preferably from 2 to 72 hours; however, it is preferable that a temporalpoint at which the raw material carboxylic acid bromodifluoroethyl ester[5] is consumed is determined, by analytical devices such as thin layerchromatography (TLC) and nuclear magnetic resonance (NMR), as theendpoint of the reaction. If the carboxylic acid bromodifluoroethylester [5] is not consumed upon spending the reaction time, the reactioncan be resumed by the further addition of water, the sulfinating agentand base upon separating a reaction solution into two layers andremoving a water layer.

By the way, in the cases where a cation moiety of the sulfinating agentis identical with that of an inorganic base (e.g. “the case of usingsodium dithionite as the sulfinating agent, and sodium carbonate as theinorganic base”, “the case of using potassium sulfite as the sulfinatingagent, and potassium hydrogencarbonate as the inorganic base” and thelike), a 2-alkylcarbonyloxy-1,1-difluoroethanesulfinic acid saltrepresented by the formula [6] can be obtained as a single product.

In such cases a further purification by recrystallization process or thelike is possible, upon treating the reaction solution by concentrationor the like.

If the cation moiety of the sulfinating agent and that of the inorganicbase are not identical, the product is not single one in the strictdefinition but a mixture of cation derived from the sulfinating agentand that derived from the inorganic base, in the formula [6]. The ratiobetween the cations differs according to the ratio between the usedsulfinating agent and the used inorganic base and to the reactionconditions. When the product is such a mixture, purification by usingrecrystallization or the like is in general difficult. To bring such acation mixture to the next step as it is possible but makes analysis,purification and the like hard to be done. Therefore, when using theinorganic base as a base, it is preferable to use the sulfinating agentand the inorganic base whose cations are identical with each other.

Then, the 4th step of the present invention will be discussed. The 4thstep is a step of reacting the2-alkylcarbonyloxy-1,1-difluoroethanesulfinic acid salt [6] obtained inthe 3rd step with an oxidizing agent thereby obtaining a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt represented bythe formula [2] (an oxidation step).

An example of the oxidizing agent used in this step is hydrogenperoxide, and additionally m-chloroperbenzoic acid, t-butylhydroperoxide, potassium peroxydisulfate, potassium permanganate, sodiumperborate, m-sodium iodate, chromic acid, sodium dichromate, halogen,iodobenzene dichloride, iodobenzene diacetate, osmium (VIII) oxide,ruthenium (VIII) oxide, sodium hypochlorite, sodium chlorite, oxide gasand ozone gas, preferably hydrogen peroxide, m-chloroperbenzoic acid andt-butyl hydroperoxide.

The molar ratio of oxidizing agent to a2-alkylcarbonyloxy-1,1-difluoroethanesulfinic acid salt [6] is normallyfrom 0.9 to 10.0, preferably from 1.0 to 2.0. Sulfinic acid saltsserving as the raw material are rough substances so that the exactnumber of moles may not be clear, in which case the oxidizing agent ispreferably added relative to the molar amount of carboxylic acidbromodifluoroethyl ester represented by the formula [5].

Furthermore, the oxidizing agent can be used in combination with atransition metal catalyst. Examples of the transition metal catalyst aredisodium tungstate, iron (III) chloride, ruthenium (III) chloride andselenium (IV) oxide, and preferably disodium tungstate.

The molar ratio of the transition metal catalyst to the2-alkylcarbonyloxy-1,1-difluoroethanesulfinic acid salt is normally from0.0001 to 1.0, preferably from 0.001 to 0.5, and more preferably from0.001 to 0.1.

Moreover, in addition to the oxidizing agent and the transition metalcatalyst, a buffer solution may be used for the purpose of adjusting thepH of the reaction solution. Examples of the buffer solution includedisodium hydrogenphosphate, sodium dihydrogenphosphate, dipotassiumhydrogenphosphate, and potassium dihydrogenphosphate. The molar ratio ofthe buffer solution to the 2-alkylcarbonyloxy-1,1-difluoroethanesulfinicacid salt is normally from 0.01 to 2.0, preferably from 0.03 to 1.0,more preferably from 0.05 to 0.5.

This reaction is usually conducted in a reaction solvent. Preferableexamples of the reaction solvent are an organic solvent such as loweralcohols, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide,acetonitrile, dimethyl sulfoxide, acetic acid and trifluoroacetic acid,in addition to water. The more preferable are water, methanol,N,N-dimethylacetamide, acetonitrile and dimethyl sulfoxide. Theparticularly preferable are water and methanol.

Additionally, the organic solvent and water may be used in combinationas necessary, in which case the ratio of the organic solvent to be usedis normally not less than 5 parts by weight, preferably not less than 10parts by weight, more preferably within a range of from 20 to 90 partsby weight relative to 100 parts by weight of total of the organicsolvent and water. The amount of the reaction solvent to be used isnormally from 1 to 100 parts by weight, preferably from 2 to 100 partsby weight, more preferably 5 to 50 parts by weight relative to 1 partsby weight of the 2-alkylcarbonyloxy-1,1-difluoroethanesulfinic acidsalt.

The reaction temperature is usually from 0 to 100° C., preferably from 5to 60° C. and more preferably from 5 to 40° C. The reaction time isusually from 0.1 to 72 hours, preferably from 0.5 to 24 hours and morepreferably from 0.5 to 12 hours; however, it is preferable that atemporal point at which the raw material2-alkylcarbonyloxy-1,1-difluoroethanesulfinic acid salt is consumed isdetermined, by analytical devices such as thin layer chromatography(TLC) and nuclear magnetic resonance (NMR), as the endpoint of thereaction.

Furthermore, the reaction solution can be brought to the next step as itis only with a treatment of such an extent as to conduct concentration,or can be purified by recrystallization or the like according tocircumstances.

Then, the 5th step of the present invention will be discussed. The 5thstep is a step of carrying out an onium-salt exchange on the2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt represented bythe formula [2] and obtained in the 4th step, by using a monovalentonium salt represented by the formula [7],

[Chemical Formula 48]

Q⁺X⁻  [7]

thereby obtaining a 2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acidonium salt represented by the formula [8] (an onium-salt exchanging step1).

Onium cation Q⁺ included in the formula [7] is expressed with asulfonium cation represented by the following formula (a) or (b), or aniodonium cation represented by the following formula (c).

In the formula (a), R¹, R² and R³ mutually independently represent asubstituted or unsubstituted linear or branched alkyl group, alkenylgroup or oxoalkyl group having 1 to 10 carbon atoms, or a substituted orunsubstituted aryl group, aralkyl group or aryloxoalkyl group having 6to 18 carbon atoms. Furthermore, any two or more of R¹, R² and R³ maybond to each other to form a ring together with a sulfur atom shown inthe formula.

In the formula (b): R⁴ represents a substituted or unsubstituted linear,branched or cyclic alkyl group or alkenyl group having 1 to 20 carbonatoms or a substituted or unsubstituted aryl group having 6 to 14 carbonatoms; m represents an integer of from 1 to 5; and n represents 0 (zero)or 1.

In the formula (c): R⁴ represents a substituted or unsubstituted linear,branched or cyclic alkyl group or alkenyl group having 1 to 20 carbonatoms or a substituted or unsubstituted aryl group having 6 to 14 carbonatoms; q represents an integer of from 0 (zero) to 5; and n represents 0(zero) or 1.

Hereinafter, a sulfonium cation represented by the formula (a) and theformula (b) and an iodonium cation represented by the formula (c) willbe discussed in detail.

Sulfonium Cation Represented by the Formula (a)

Concrete examples of R¹, R² or R³ as shown in the formula (a) are asfollows. Examples of alkyl group include methyl group, ethyl group,n-propyl group, isopropyl group, cyclopropyl group, n-butyl group,sec-butyl group, isobutyl group, tert-butyl group, n-pentyl group,cyclopentyl group, n-hexyl group, n-heptyl group, 2-ethylhexyl group,cyclohexyl group, cycloheptyl group, 4-methylcyclohexyl group,cyclohexylmethyl group, n-octyl group, n-decyl group, 1-adamantyl group,2-adamantyl group, bicyclo[2.2.1]hepten-2-yl group, 1-adamantanemethylgroup and 2-adamantanemethyl group. Examples of alkenyl group includevinyl group, allyl group, propenyl group, butenyl group, hexenyl groupand cyclohexenyl group. Examples of oxoalkyl group include2-oxocyclopentyl group, 2-oxocyclohexyl group, 2-oxopropyl group,2-cyclopentyl-2-oxoethyl group, 2-cyclohexyl-2-oxoethyl group and2-(4-methylcyclohexyl)-2-oxoethyl group. Examples of aryl group are:phenyl group; naphthyl group; thienyl group; alkoxy phenyl groups suchas p-methoxyphenyl group, m-methoxyphenyl group, o-methoxyphenyl group,p-ethoxyphenyl group, p-tert-butoxyphenyl group and m-tert-butoxyphenylgroup; alkyl phenyl group such as 2-methylphenyl group, 3-methylphenylgroup, 4-methylphenyl group and ethylphenyl group; alkyl naphthyl groupsuch as methyl naphthyl group and ethyl naphthyl group; dialkyl naphthylgroup such as diethyl naphthyl group; dialkoxy naphthyl group such asdimethoxy naphthyl group and diethoxy naphthyl group. Examples ofaralkyl group include benzyl group, 1-phenylethyl group and2-phenylethyl group. Examples of aryloxoalkyl group include2-aryl-2-oxoethyl group such as 2-phenyl-2-oxoethyl group,2-(1-naphthyl)-2-oxoethyl group and 2-(2-naphthyl)-2-oxoethyl group.Additionally, in the case where any two or more of R¹, R² and R³ bond toeach other through a sulfur atom to form a cyclic structure, theexamples include 1,4-butylene and 3-oxa-1,5-pentylene. Examples ofsubstituent are aryl groups having a polymerizable substituent such asacryloyloxy group and methacryloyloxy group, and more concretely include4-(acryloyloxy)phenyl group, 4-(methacryloyloxy)phenyl group,4-vinyloxyphenyl group and 4-vinylphenyl group.

Further concrete examples of sulfonium cation represented by the formula(a) include triphenylsulfonium, (4-tert-butylphenyl)diphenylsulfonium,bis(4-tert-butylphenyl)phenylsulfonium,tris(4-tert-butylphenyl)sulfonium,(3-tert-butylphenyl)diphenylsulfonium,bis(3-tert-butylphenyl)phenylsulfonium,tris(3-tert-butylphenyl)sulfonium,(3,4-ditert-butylphenyl)diphenylsulfonium,bis(3,4-ditert-butylphenyl)phenylsulfonium,tris(3,4-ditert-butylphenyl)sulfonium,(4-tert-butoxyphenyl)diphenylsulfonium,bis(4-tert-butoxyphenyl)phenylsulfonium,tris(4-tert-butoxyphenyl)sulfonium,(3-tert-butoxyphenyl)diphenylsulfonium,bis(3-tert-butoxyphenyl)phenylsulfonium,tris(3-tert-butoxyphenyl)sulfonium,(3,4-ditert-butoxyphenyl)diphenylsulfonium,bis(3,4-ditert-butoxyphenyl)phenylsulfonium,tris(3,4-ditert-butoxyphenyl)sulfonium,diphenyl(4-thiophenoxyphenyl)sulfonium,(4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium,tris(4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium,(4-tert-butoxyphenyl)bis(4-dimethylaminophenyl)sulfonium,tris(4-dimethylaminophenyl)sulfonium, 2-naphthyldiphenylsulfonium,dimethyl(2-naphthyl)sulfonium, (4-hydroxyphenyl)dimethylsulfonium,(4-methoxyphenyl)dimethylsulfonium, trimethylsulfonium,(2-oxocyclohexyl)cyclohexylmethylsulfonium, trinaphthylsulfonium,tribenzylsulfonium, diphenylmethylsulfonium, dimethylphenylsulfonium,2-oxo-2-phenylethylthiacyclopentanium, diphenyl-2-thienylsulfonium,4-n-butoxynaphthyl-1-thiacyclopentanium,2-n-butoxynaphthyl-1-thiacyclopentanium,4-methoxynaphthyl-1-thiacyclopentanium, and2-methoxynaphthyl-1-thiacyclopentanium. More preferable examples aretriphenylsulfonium, (4-tert-butylphenyl)diphenylsulfonium,(4-tert-butoxyphenyl)diphenylsulfonium,tris(4-tert-butylphenyl)sulfonium and(4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium.

Still further examples thereof are4-(methacryloyloxy)phenyldiphenylsulfonium,4-(acryloyloxy)phenyldiphenylsulfonium,4-(methacryloyloxy)phenyldimethylsulfonium, and4-(acryloyloxy)phenyldimethylsulfonium. Regarding these polymerizablesulfonium cation, Japanese Patent Application Publication No. 4-230645,Japanese Patent Application Publication 2005-84365 and the like can bereferred to.

Sulfonium Cation Represented by the Formula (b)

In the formula (b), R⁴—(O)_(n)— group is not particularly limited inmoiety at which R⁴—(O)_(n)— group serves as a substituent, butpreferably occupies position 4 or 3, more preferably position 4 ofphenyl group. In the formula, n represents 0 (zero) or 1. Concreteexamples of R⁴ include methyl group, ethyl group, n-propyl group,sec-propyl group, cyclopropyl group, n-butyl group, sec-butyl group,isobutyl group, tert-butyl group, n-pentyl group, cyclopentyl group,n-hexyl group, cyclohexyl group, n-octyl group, n-decyl group, n-dodecylgroup, 1-adamantyl group, 2-adamantyl group, bicyclo[2.2.1]hepten-2-ylgroup, phenyl group, 4-methoxyphenyl group, 4-tert-butylphenyl group,4-biphenyl group, 1-naphthyl group, 2-naphthyl group, 10-anthranyl groupand 2-furanyl group. In the case of n=1, the examples further includeacryloyl group, methacryloyl group, vinyl group and allyl group.

Concrete examples of sulfonium cation are(4-methylphenyl)diphenylsulfonium, (4-ethylphenyl)diphenylsulfonium,(4-cyclohexylphenyl)diphenylsulfonium,(4-n-hexylphenyl)diphenylsulfonium, (4-n-octyl)phenyldiphenylsulfonium,(4-methoxyphenyl)diphenylsulfonium, (4-ethoxyphenyl)diphenylsulfonium,(4-tert-butoxyphenyl)diphenylsulfonium,(4-cyclohexyloxyphenyl)diphenylsulfonium,(4-trifluoromethylphenyl)diphenylsulfonium,(4-trifluoromethyloxyphenyl)diphenylsulfonium, and(4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium.

Iodonium Cation Represented by the Formula (c)

In the formula (c), R⁴—(O)_(n)— group is not particularly limited inmoiety at which R⁴—(O)_(n)— group serves as a substituent, butpreferably occupies position 4 or 3, more preferably position 4 ofphenyl group. In the formula, n represents 0 (zero) or 1. Concreteexamples of R⁴ are the same as those discussed in the above formula (b).

Concrete examples of iodonium cation include diphenyliodonium,bis(4-methylphenyl)iodonium, bis(4-ethylphenyl)iodonium,bis(4-tert-butylphenyl)iodonium,bis(4-(1,1-dimethylpropyl)phenyl)iodonium,(4-methoxyphenyl)phenyliodonium, (4-tert-butoxyphenyl)phenyliodonium,(4-acryloyloxy)phenylphenyliodonium, and(4-methacryloyloxy)phenylphenyliodonium. Among these,bis(4-tert-butylphenyl)iodonium is preferably used.

Additionally, examples of a monovalent anion represented in the formula[7] by X⁻ include F⁻, CI⁻, Br⁻, I⁻, ClO₄ ⁻, HSO₄ ⁻, H₂PO₄ ⁻, BF₄ ⁻, PF₆⁻, SbF₆ ⁻, aliphatic sulfonic acid anion, aromatic sulfonic acid anion,trifluoromethanesulfonic acid anion, fluorosulfonic acid anion,aliphatic carboxylic acid anion, aromatic carboxylic acid anion,fluorocarboxylic acid anion and trifluoroacetic acid anion. Thepreferable are Cl⁻, Br⁻, HSO₄ ⁻, BF₄ ⁻, aliphatic sulfonic acid and thelike. The more preferable are Cl⁻, Br⁻ and HSO₄ ⁻.

The molar ratio of a monovalent onium salt represented in the formula[7] to a 2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt [2] (or[22]) is usually from 0.5 to 10.0, preferably from 0.8 to 2.0 and morepreferably from 0.9 to 1.2.

This reaction is usually conducted in a reaction solvent. Preferableexamples of the reaction solvent are an organic solvent such as loweralcohols, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide,acetonitrile and dimethyl sulfoxide, in addition to water. The morepreferable are water, methanol, N,N-dimethylacetamide, acetonitrile anddimethyl sulfoxide. The particularly preferable is water.

Additionally, the organic solvent and water may be used in combinationas necessary, in which case the ratio of the organic solvent to be usedis normally not less than 5 parts by weight, preferably not less than 10parts by weight, more preferably within a range of from 20 to 90 partsby weight relative to 100 parts by weight of total of the organicsolvent and water. The amount of the reaction solvent to be used isnormally from 1 to 100 parts by weight, preferably from 2 to 100 partsby weight, more preferably 5 to 50 parts by weight relative to 1 partsby weight of a counter ion exchange precursor.

The reaction temperature is usually from 0 to 80° C., preferably from 5to 30° C. The reaction time is usually from 10 minutes to 16 hours,preferably from 30 minutes to 6 hours; however, it is preferable that atemporal point at which the raw material2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt [2] (or [22]) isconsumed is determined, by analytical devices such as thin layerchromatography (TLC) and nuclear magnetic resonance (NMR), as theendpoint of the reaction.

The thus obtained 2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acidonium salt represented by the formula [8] can be rinsed with an organicsolvent or can be extracted to be purified. Examples of the organicsolvent are preferably those who are not to be mixed with water,including: esters such as ethyl acetate and n-butyl acetate; ethers suchas diethyl ether; halogenated alkyls such as methylene chloride andchloroform.

By the process as had been discussed, a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid onium salt not havingin its structure an unconjugated unsaturated moiety (a double or triplebond) as a substituent for acyl group. This compound can be provided asa photoacid generator used to a chemically amplified resist material.Those who have in its structure an unconjugated unsaturated moiety (adouble or triple bond) as a substituent for acyl group are hard to beproduced by the above steps so as to need to conduct further steps asbelow thereon.

Then, the 5′th step of the present invention will be discussed. The 5′thstep is a step of saponifying (i.e. hydrolyzing in the presence of basicsubstance) the 2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid saltrepresented by the formula [2] and obtained in the 4th step therebyobtaining a 2-hydroxy-1,1-difluoroethanesulfonic acid salt representedby the formula [9] (a saponification step).

A process for saponifying a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt represented bythe formula [2] is not particularly limited and therefore adopted fromany of commonly known saponification processes. Examples thereof are asfollows.

In general, saponification reaction is conducted in the presence of abasic catalyst in which hydroxide, bicarbonate and carbonate of one ormore kinds of alkali metals, ammonia, amine compounds are included as abase. Examples of alkali metal compounds are sodium hydroxide, potassiumhydroxide, lithium hydroxide, sodium hydrogencarbonate, potassiumhydrogencarbonate, sodium carbonate and potassium carbonate. Examples ofamine compounds are methylamine, dimethylamine, trimethylamine,ethylamine, diethylamine, triethylamine, propylamine, dipropylamine,tripropylamine, butylamine, dibutylamine, tributylamine,cyclohexylamine, benzylamine, morpholine, pyrrole, pyrrolidine,pyridine, ethanolamine, diethanolamine, triethanolamine,N,N-dimethylaminoethanol, N,N-diethylaminoethanol, ethylenediamine,diethylenetriamine, triethylenetetramine, 1,2-propylenediamine,dipropylenetriamine and tripropylenetetramine, and quaternary ammoniumhydroxide salts of these.

The molar ratio of the base to a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt [2] is usuallyfrom 0.01 to 10.0, preferably from 0.1 to 5.0 and more preferably from0.5 to 2.0.

This reaction is usually conducted in the presence of water. The molarratio of water to a 2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acidsalt [2] is usually not less than 1 and has no upper limit. However, themolar ratio is preferably not more than 100 and more preferably not morethan 50, since the use of an excessively large quantity of water reducesefficiency.

Additionally, water can be used in combination with an organic solventas necessary, in which case the organic solvent to be used incombination are not particularly limited, but preferably those who canextract a 2-hydroxy-1,1-difluoroethanesulfonic acid salt represented bythe formula [9] from a water layer. Examples of the organic solvent arepreferably those who are not to be mixed with water, including: esterssuch as ethyl acetate and n-butyl acetate; ethers such as diethyl ether;and halogenated alkyls such as methylene chloride and chloroform.

In this case, the amount of the organic solvent is normally not lessthan 5 parts by weight, preferably not less than 10 parts by weight,more preferably within a range of from 20 to 90 parts by weight relativeto 100 parts by weight of total of the organic solvents and water.

The reaction temperature is usually from 0 to 100° C., preferably from 5to 80° C. The reaction time is usually from 10 minutes to 16 hours andpreferably from 30 minutes to 6 hours; however, it is preferable that atemporal point at which the raw material2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt [2] is consumedis determined, by analytical devices such as thin layer chromatography(TLC) and nuclear magnetic resonance (NMR), as the endpoint of thereaction.

The thus obtained 2-hydroxy-1,1-difluoroethanesulfonic acid saltrepresented by the formula [9] can be extracted with the organic solventor purified by recrystallization, as necessary.

Then, the 6th step of the present invention will be discussed. The 6thstep is a step of reacting the 2-hydroxy-1,1-difluoroethanesulfonic acidsalt represented by the formula [9] with a carboxylic acid derivativerepresented by the formula [10] or the formula [11] to causeesterification, thereby producing a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt represented bythe formula [12] ([a 6th step]: an esterification step 2).

Examples of R′ shown in the formula [10] or the formula [11] are thesame as those of R discussed above; however, R′ is different from R inthat its substituent may be exemplified further by linear, branched orcyclic alkenyl group. Concrete examples of alkenyl group are vinylgroup, allyl group, 1-methylethenyl group, 1-methylallyl group,2-methylallyl group, 1-propenyl group, isopropenyl group, 2-butenylgroup, 3-butenyl group, 1,3-butadienyl group, 2-pentenyl group,4-pentenyl group, 2-hexenyl group, 5-hexenyl group, cyclopropenyl group,cyclopentenyl group, cyclohexenyl group and 5-norbornen-1-yl group.

A 2-hydroxy-1,1-difluoroethanesulfonic acid salt [9] hardly dissolves ina hydrocarbon-based nonpolar solvent such as n-hexane, benzene andtoluene so as not to be preferably used as the solvent used in thisstep. It is preferable to use: water; a ketone-based solvent such asmethyl ethyl ketone and methyl isobutyl ketone; an ester-based solventsuch as ethyl acetate and butyl acetate; an ether-based solvent such asdiethyl ether, diethylene glycol dimethyl ether, tetrahydrofuran anddioxane; a halogen-based solvent such as dichloromethane, chloroform,carbon tetrachloride, 1,2-dichloroethane, tetrachloroethylene,chlorobenzene and ortho-chlorobenzene; and a polar solvent such asacetonitrile, N,N-dimethylformamide, N,N-dimethylimidazolidinone,dimethyl sulfoxide and sulfolane.

As discussed above, a 2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acidsalt represented by the formula [12] can be produced from a2-hydroxy-1,1-difluoroethanesulfonic acid salt represented by theformula [9] by using: carboxylic acids or carboxylic acid halidesrepresented by the formula [10] instead of carboxylic acids orcarboxylic acid halides represented by the formula [3]; carboxylic acidanhydrides represented by the formula [11] instead of carboxylic acidanhydrides represented by the formula [4]; and the process generallysimilar to that in the 2nd step with the exception of slightly limitingthe solvent to be used.

Upon termination of the reaction, a2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt represented bythe formula [12] can be obtained by normal means including extraction,solvent concentration and the like. Moreover, it can be purified bycolumn chromatography, recrystallization or the like, as necessary.

Then, the 7th step of the present invention will be discussed. The 7thstep is a step of carrying out an onium-salt exchange by using amonovalent onium salt represented by the formula [7] on the2-alkylcarbonyloxy-1,1-difluoroethanesulfonic acid salt represented bythe formula [12] and obtained in the 6th step, thereby obtaining a2-hydroxy-1,1-difluoroethanesulfonic acid onium salt represented by theformula [13] (an onium-salt exchanging step 2). This step can beconducted in a similar manner to the 5th step (an onium-salt exchangingstep 1).

By the way, the 6th step and the 7th step can be conducted in thereverse order (Equation [17]).

[Chemical Formula 52]

Namely, it is a process for carrying out an onium-salt exchange by usinga monovalent onium salt represented by the formula [7] on a2-hydroxy-1,1-difluoroethanesulfonic acid salt represented by theformula [9] to obtain a 2-hydroxy-1,1-difluoroethanesulfonic acid oniumsalt (a 6′th step: an onium-salt exchanging step 2), followed byesterification, thereby producing a 2-hydroxy-1,1-difluoroethanesulfonicacid onium salt represented by the formula [13] (a 7′th step: anesterification step 2).

This process, however, requires to use an enormously excessive amount ofonium salt in the 6′th step, and additionally has had some disadvantagessuch as difficulty in purifying a 2-hydroxy-1,1-difluoroethanesulfonicacid onium salt represented by the formula [13] (Comparative Example 1).

Accordingly, it is a preferable process to conduct the 6th step and the7th step in this order.

The present invention will be more specifically discussed with referenceto the following Examples; however, the present invention is not limitedby these Examples.

EXAMPLE 1 [Production of 2-bromo-2,2-difluoroethanol] (a 1st Step: aReduction Step)

A glass flask equipped with a thermometer, a condenser and a droppingfunnel was charged with 186 g (4.91 moles) of sodium borohydride, 425 g(13.2 moles) of methanol and 3 L of diisopropyl ether, followed bystirring. Then, a diisopropyl ether solution (1 L) of 1000 g (4.92moles) of ethyl bromodifluoroacetate was added thereto dropwise in aniced bath. After the termination of the dropping, stirring was conductedfor 1 hour at room temperature. Then, the termination of the reactionwas confirmed by gas chromatography. The reaction solution was separatedinto an organic layer and a water layer after the addition of 2.5 L of2N hydrochloric acid, followed by extracting the water layer with 500 mlof diisopropyl ether. Subsequently, the organic layer was rinsed with500 ml of saturated sodium hydrogencarbonate and 500 ml of saturatedbrine. Upon drying with anhydrous sodium sulfate, a solvent wasdistilled off and a precise distillation was performed, therebyobtaining 430 g (54% yield, 99% purity) of 2-bromo-2,2-difluoroethanolin the form of a colorless and transparent liquid.

EXAMPLE 2 [Production of 2-bromo-2,2-difluoroethanol] (a 1st Step: aReduction Step)

A glass flask equipped with a thermometer, a condenser and a droppingfunnel was charged with 6 g (29.6 millimoles) of ethylbromodifluoroacetate and 25 g of dehydrogenated diglyme, followed bystirring. Then, 1.5 g (39.5 millimoles) of lithium aluminohydride(LiAlH₄) was added thereto. It was heated to 60° C. and stirred for 12hours, followed by cooling to room temperature, and then extraction wascarried out thereon with the addition of diisopropyl ether andhydrochloric acid (1M). Upon separating into two layers, an organiclayer was rinsed with saturated sodium bicarbonate water, saturatedbrine and water, followed by drying with magnesium sulfate. Afterfiltration, a solvent was distilled off under a reduced pressure,thereby obtaining 3.8 g of the target 2-bromo-2,2-difluoroethanol (80%yield, 95% purity).

EXAMPLE 3 [Production of 2-bromo-2,2-difluoroethanol] (a 1st Step: aReduction Step)

A glass flask equipped with a thermometer, a condenser and a droppingfunnel was charged with 27 g (140 millimoles) of ethylbromodifluoroacetyl chloride and 200 g of tetrahydrofuran, followed bystirring. Then, 5.0 g (132 moles) of sodium borohydride (NaBH₄) wasadded thereto. It was heated to 60° C. and stirred for 16 hours,followed by cooling to room temperature, and then extraction was carriedout thereon with the addition of diisopropyl ether and hydrochloric acid(1M). Upon separating into two layers, an organic layer was rinsed withsaturated sodium bicarbonate water, saturated brine and water, followedby drying with magnesium sulfate. After filtration, a solvent wasdistilled off under a reduced pressure, thereby obtaining 19.2 g of thetarget 2-bromo-2,2-difluoroethanol (85% yield, 96% purity).

EXAMPLE 4-1 [Production of 2-bromo-2,2-difluoroethyl pivalate] (a 2ndStep: Esterification Step)

A glass flask equipped with a thermometer, a condenser and a droppingfunnel was charged with 271 g (2.24 moles) of pivaloyl chloride, 360 g(2.23 moles) of 2-bromo-2,2-difluoroethanol and 1.5 L of diisopropylether, followed by stirring. Then, 318 g (3.14 moles) of triethylaminewas added dropwise thereto, in an iced bath. After the termination ofthe dropping, stirring was conducted for 1 hour at room temperature.Then, the termination of the reaction was confirmed by gaschromatography. With the addition of 300 mL of water, a reactionsolution was completely dissolved therein, followed by adding 500 mL of2N hydrochloric acid thereto. The reaction solution was separated intoan organic layer and a water layer, followed by extracting the waterlayer with 500 ml of diisopropyl ether. Subsequently, the organic layerwas rinsed with 500 ml of saturated brine. Upon drying with anhydroussodium sulfate, a solvent was distilled off, thereby obtaining 485 g(82% yield, 93% purity) of 2-bromo-2,2-difluoroethanol in the form of alight yellow liquid.

Properties of 2-bromo-2,2-difluoroethyl pivalate

¹H NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Tetramethylsilane); δ=4.52 (t, 2H), 1.19 (s, 9H).

¹⁹F NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Trichlorofluoromethane); δ=−56.6 (t, 2F).

EXAMPLE 4-2 [Production of sodium1,1-difluoro-2-(pivaloyloxy)ethanesulfinic acid] (a 3rd Step: aSulfination Step)

A glass flask equipped with a thermometer and a condenser was chargedwith 376 g (1.24 moles) of 2-bromo-2,2-difluoroethyl pivalate, 154 g(1.83 moles) of sodium hydrogencarbonate, 319 g (1.83 moles) of sodiumdithionite, 1.2 L of acetonitrile and 1.2 L of water, followed bystirring for 4 hours at 70° C. It was cooled to room temperature and awater layer was eliminated therefrom. Thereafter 154 g (1.83 moles) ofsodium hydrogencarbonate, 319 g (1.83 moles) of sodium dithionite and1.2 L of water were added, followed by stirring for 4 hours at 70° C.This operation was further repeated two times. The termination of thereaction was confirmed by ¹⁹F NMR. An organic layer was separated from areaction solution consisting of two layers and concentration and dryingwere conducted thereon, thereby obtaining 290 g of sodium1,1-difluoro-2-(pivaloyloxy)ethanesulfinic acid in the form of a whitesolid (60% yield, 65% purity).

Properties of sodium 1,1-difluoro-2-(pivaloyloxy)ethanesulfinic acid

¹H NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Tetramethylsilane); δ=4.41 (t, 2H), 1.14 (s, 9H).

¹⁹F NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Trichlorofluoromethane); δ=−120.2 (t, 2F).

EXAMPLE 4-3 [Production of sodium1,1-difluoro-2-(pivaloyloxy)ethanesulfonate] (a 4th Step: an OxidationStep)

A glass flask equipped with a thermometer, a condenser and a droppingfunnel was charged with 290 g (0.74 mole) of 65% purity sodium1,1-difluoro-2-(pivaloyloxy)ethane-1-sulfinate, a catalytic amount ofsodium tungstate (IV) dihydrate, 600 ml of water, followed by stirring.Then, 170 g (1.5 moles) of 30% oxygenate was added dropwise in an icedbath. After the termination of the dropping, stirring was conducted for1 hour at room temperature. Then, the termination of the reaction wasconfirmed by ¹⁹F NMR. The reaction solution was concentrated and thenrinsed with 500 ml of diisopropyl ether. Subsequently, filtration wasconducted and a solid obtained therewith was dried, thereby obtaining278 g of sodium 1,1-difluoro-2-(pivaloyloxy)ethanesulfonate in the formof a white solid (91% yield, 65% purity).

Properties of sodium 1,1-difluoro-2-(pivaloyloxy)ethanesulfonate

¹H NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Tetramethylsilane); δ=4.52 (t, 2H), 1.15 (s, 9H).

¹⁹F NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Trichlorofluoromethane); δ=−113.8 (t, 2F).

EXAMPLE 5-1 [Production of 2-bromo-2,2,-difluoroethyl valerate] (a 2ndStep: an Esterification Step 1)

A 200 mL reactor was charged under nitrogen with 6.0 g (50.0 millimoles)of valeryl chloride and 90 mL of THF (dehydrated) and then put into aniced bath, to which 11.3 g (93% purity, 65.3 millimoles/1.31equivalents) of 2-bromo-2,2,-difluoroethanol was added and then 7.1 g(70.0 millimoles/1.4 equivalents) of triethylamine was added dropwise.After the dropping, stirring was conducted at room temperature for 18hours. Thereafter 35 ml of water was added thereto and extraction wascarried out two times with 100 mL of diisopropyl ether. The obtainedorganic layer was further rinsed with diluted hydrochloric acid, sodiumbicarbonate water and brine. Then, water content was eliminated withsodium sulfate, followed by filtration. Upon this, isopropyl ether wasdistilled off thereby obtaining 9.9 g of the target(2-bromo-2,2,-difluoro)ethyl valerate. In this case, purity was 89% andyield was 72%.

Properties of (2-bromo-2,2,-difluoro)ethyl valerate

¹H NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Tetramethylsilane); δ=4.53 (t, J=11.6 Hz, 2H; CH₂), 2.36 (t,J=7.6 Hz, 2H; CH₂), 1.59 (quintet, J=7.6 Hz, 2H; CH₂), 1.31 (sextet,J=7.6 Hz, 2H; CH₂), 0.86 (t, J=7.6 Hz, 3H; CH₃).

¹⁹F NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Trichlorofluoromethane); δ=−56.74 (t, J=11.6 Hz, 2F; CF₂).

EXAMPLE 5-2 [Production of sodium1,1-difluoro-2-(valeryloxy)ethanesulfinate] (a 3rd Step: a SulfinationStep)

A 200 mL reactor was charged under nitrogen with 9.7 g (89% purity, 35.4millimoles) of (2-bromo-2,2,-difluoro)ethyl valerate, 40 g ofacetonitrile, 5.9 g (70.7 millimoles/2.0 equivalents) of sodiumhydrogencarbonate, 8.7 g (50.1 millimoles/1.5 equivalents) of sodiumdithionite and 40 g of water, followed by stirring at 60° C. for 1.5hours and at 80° C. for 16 hours. The reactor was further charged with5.9 g (70.7 millimoles) of sodium hydrogencarbonate and 8.7 g (50.1millimoles) of sodium dithionite, followed by stirring at 80° C. for 94hours. Extraction was conducted on a reaction solution six times with 40mL of acetonitrile and then a solvent was distilled out of the obtainedorganic layer, followed by rinsing with 200 mL of diisopropyl ether.Then, filtration was conducted thereon, followed by drying a solid,thereby obtaining 6.74 g of the target sodium2-valeryloxy-1,1-difluoroethanesulfinate. In this case, purity was 28%and yield was 21%.

Properties of sodium 2-valeryloxy-1,1-difluoroethanesulfinate

¹H NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Tetramethylsilane); δ=4.42 (t, J=16.4 Hz, 2H; CH₂), 2.34 (t,J=7.6 Hz, 2H; CH₂), 1.50 (quintet, J=7.6 Hz, 2H; CH₂), 1.28 (sextet,J=7.6 Hz, 2H; CH₂), 0.85 (t, J=7.6 Hz, 3H; CH₃).

¹⁹F NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Trichlorofluoromethane); δ=−119.95 (t, J=16.4 Hz, 2F; CF₂).

EXAMPLE 5-3 [Production of sodium1,1-difluoro-2-(valeryloxy)ethanesulfonate] (a 4th Step: an OxidationStep)

A 100 mL reactor was charged with 6.6 g (28% purity, 7.3 millimoles) ofsodium 2-valeryloxy-1,1-difluoroethanesulfinate, 60 mL of water, 0.0047g (0.014 millimole/0.0019 equivalent) of disodium tungstate dihydrateand 1.9 g (16.4 millimoles/2.25 equivalents) of 30% oxygenate, followedby stirring at room temperature for 1.5 hours. A reaction solution washeated under a reduced pressure to evaporate a volatile component todryness, thereby obtaining 6.6 g of the target sodium2-valeryloxy-1,1-difluoroethane sulfonate. In this case, purity was 26%and yield was 88%.

Properties of sodium 2-valeryloxy-1,1-difluoroethane sulfonate

¹H NMR (Solvent for measurement: Deuterated DMSO, Reference material:Tetramethylsilane); δ=4.52 (t, J=15.6 Hz, 2H; CH₂), 2.34 (t, J=7.6 Hz,2H; CH₂), 1.51 (quintet, J=7.6 Hz, 2H; CH₂), 1.28 (sextet, J=7.6 Hz, 2H;CH₂), 0.85 (t, J=7.6 Hz, 3H; CH₃).

¹⁹F NMR (Solvent for measurement: Deuterated DMSO, Reference material:Trichlorofluoromethane); δ=−113.70 (t, J=15.6 Hz, 2F; CF₂).

EXAMPLE 6-1 [Production of 2′-bromo-2′,2′-difluoroethyl1-adamantanecarboxylate] (a 2nd Step: an Esterification Step 1)

A 300 mL reactor was charged under nitrogen with 14.2 g (71.3millimoles) of 1-adamantanecarbonyl chloride and 120 mL of THF(dehydrated), followed by putting it in an iced bath. There 16.1 g (92%purity, 91.8 millimoles/1.29 equivalents) of 2-bromo-2,2-difluoroethanolwas added, and 10.1 g (99.8 millimoles/1.4 equivalents) of triethylaminewas added dropwise. After the dropping, stirring was conducted at 60° C.for 23 hours. Then, 50 mL of water was added, and extraction wasconducted two times with 150 mL of diisopropyl ether. The obtainedorganic layer was further rinsed with diluted hydrochloric acid, sodiumbicarbonate water and brine, followed by removing water content withsodium sulfate, filtration, and then distilling isopropyl ether off,thereby obtaining 23.2 g of the target 2′-bromo-2′,2′-difluoroethyl1-adamantanecarboxylate. In this case, purity was 85%, and yield was86%.

Properties of 2′-bromo-2′,2′-difluoroethyl 1-adamantanecarboxylate

¹H NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Tetramethylsilane); δ=4.51 (t, J=11.6 Hz, 2H; CH₂), 1.97 (m,3H; 1-Ad), 1.87 (m, 6H; 1-Ad), 1.66 (m, 6H; 1-Ad).

¹⁹F NMR (Solvent for measurement: Deuterated chloroform, Referencematerial: Trichlorofluoromethane); δ=−56.46 (t, J=11.6 Hz, 2F; CF₂).

EXAMPLE 6-2 [Production of sodium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfinate] (a 3rd Step: aSulfination Step)

A 300 mL vessel was charged under nitrogen with 22.8 g (85% purity, 60.0millimoles) of 2′-bromo-2′,2′-difluoroethyl 1-adamantanecarboxylate, 80g of acetonitrile, 10.1 g (120 millimoles/2.0 equivalents) of sodiumhydrogencarbonate, 15.7 g (90.0 millimoles/1.5 equivalents) of sodiumdithionite and 80 g of water, followed by stirring at 70° C. for 66hours. The reactor was further charged with 6.7 g (80.0 millimoles) ofsodium hydrogencarbonate and 10.5 g (60.0 millimoles) of sodiumdithionite, followed by stirring at 80° C. for 24 hours. Extraction wasconducted on a reaction solution one time with 30 mL of acetonitrile andthen a solvent was distilled out of the obtained organic layer, followedby rinsing with 400 mL of diisopropyl ether. Then, filtration wasconducted thereon, followed by drying a solid, thereby obtaining 12.0 gof the target sodium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfinate. In this case,purity was 65%. Furthermore, the solvent was distilled out of a rinsingliquid thereby recovering 11.3 g of (2′-bromo-2′,2′-difluoro)ethyl1-adamantanecarboxylate. In this case purity was 71%.

A 200 mL vessel was charged under nitrogen with 11.1 g (71% purity, 24.4millimoles) of the recovered (2′-bromo-2′,2′-difluoro)ethyl1-adamantanecarboxylate, 40 g of acetonitrile, 4.1 g (48.8millimoles/2.0 equivalents) of sodium hydrogencarbonate, 6.4 g (36.6millimoles/1.5 equivalents) of sodium dithionite and 40 g of water,followed by stirring at 80° C. for 18 hours. The reactor was furthercharged with 1.9 g (22.4 millimoles) of sodium hydrogencarbonate and 2.9g (16.8 millimoles) of sodium dithionite, followed by stirring at 80° C.for 22 hours. Extraction was conducted on a reaction solution one timewith 30 mL of acetonitrile and then a solvent was distilled out of theobtained organic layer, followed by rinsing with 250 mL of diisopropylether. Then, filtration was conducted thereon, followed by drying asolid, thereby obtaining 6.9 g of the target sodium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfinate. In this case,purity was 61%.

Properties of sodium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfinate

¹H NMR (Solvent for measurement: Deuterated DMSO, Reference material:Tetramethylsilane); δ=4.42 (t, J=16.4 Hz, 2H; CH₂), 1.93 (m, 3H; 1-Ad),1.80 (m, 6H; 1-Ad), 1.63 (m, 6H; 1-Ad).

¹⁹F NMR (Solvent for measurement: Deuterated DMSO, Reference material:Trichlorofluoromethane); δ=−120.23 (t, J=16.4 Hz, 2F; CF₂).

EXAMPLE 6-3 [Production of sodium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate] (a 4th Step:an Oxidation Step)

A 300 mL reactor was charged with 18.6 g (64% purity, 36.0 millimoles)of sodium 2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfinate, 120mL of water, 0.0154 g (0.047 millimole/0.0013 equivalent) of disodiumtungstate dihydrate and 6.1 g (53.9 millimoles/1.5 equivalents) of 30%oxygenate, followed by stirring at room temperature for 2 hours. Areaction solution was heated under a reduced pressure to evaporate avolatile component to dryness, thereby obtaining 18.6 g of the targetsodium 2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate. In thiscase, purity was 65% and yield was 97%.

Properties of sodium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate

¹H NMR (Solvent for measurement: Deuterated DMSO, Reference material:Tetramethylsilane); δ=4.51 (t, J=15.3 Hz, 2H; CH₂), 1.96 (m, 3H; 1-Ad),1.82 (m, 6H; 1-Ad), 1.65 (m, 6H; 1-Ad).

¹⁹F NMR (Solvent for measurement: Deuterated DMSO, Reference material:Trichlorofluoromethane); δ=−113.94 (t, J=16.4 Hz, 2F; CF₂).

EXAMPLE 7 [Production of triphenylsulfonium1,1-difluoro-2-(valeryloxy)ethanesulfonate] (a 5th Step: an Onium-SaltExchanging Step 1)

A 100 mL reactor was charged with 3.0 g (26% purity, 2.9 millimoles) ofsodium 1,1-difluoro-2-(valeryloxy)ethanesulfonate obtained in Example5-3 and 30 g of water, followed by adding dropwise an aqueous solutionof triphenylsulfonium chloride [17.8 g (5.2 millimoles/1.8 equivalents)of triphenylsulfonium chloride and 16.2 g of water] at room temperature,followed by stirring at room temperature for 1.5 hours. Then, extractionwas conducted by adding 30 mL of chloroform. The obtained organic layerwas rinsed two times with water, followed by distilling a solvent off,thereby obtaining 0.96 g of the target triphenylsulfonium1,1-difluoro-2-(valeryloxy)ethanesulfonate.

In this case, purity was 98%, and yield was 64%.

Properties of triphenylsulfonium1,1-difluoro-2-(valeryloxy)ethanesulfonate

¹H NMR (Solvent for measurement: Deuterated DMSO, Reference material:Tetramethylsilane); δ=7.92-7.70 (m, 15H, Ph₃S⁺), 4.52 (t, J=15.6 Hz, 2H;CH₂), 2.36 (t, J=7.2 Hz, 2H; CH₂), 1.49 (quintet, J=7.2 Hz, 2H; CH₂),1.28 (sextet, J=7.2 Hz, 2H; CH₂), 0.85 (t, J=7.2 Hz, 3H; CH₃).

¹⁹F NMR (Solvent for measurement: Deuterated DMSO, Reference material:Trichlorofluoromethane); δ=−113.72 (t, J=15.6 Hz, 2F; CF₂).

EXAMPLE 8 [Production of triphenylsulfonium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate] (a 5th Step:an Onium-Salt Exchanging Step 1)

A 200 mL reactor was charged with 9.5 g (65% purity, 17.8 millimoles) ofsodium 2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate obtainedin Example 6-3 and 85 g of water, followed by adding dropwise an aqueoussolution of triphenylsulfonium chloride [5.6 g (19.6 millimoles/1.1equivalents) of triphenylsulfonium chloride and 61.7 g of water] at roomtemperature, followed by stirring at room temperature for 1.5 hours.Then, filtration was conducted and then a solid was dried, therebyobtaining 9.8 g of the target triphenylsulfonium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate. In this case,purity was 98%, and yield was 92%.

Properties of triphenylsulfonium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate

¹H NMR (Solvent for measurement: Deuterated DMSO, Reference material:Tetramethylsilane); δ=7.91-7.72 (m, 15H, Ph₃S⁺), 4.51 (t, J=15.3 Hz, 2H;CH₂), 1.96 (m, 3H; 1-Ad), 1.82 (m, 6H; 1-Ad), 1.65 (m, 6H; 1-Ad).

¹⁹F NMR (Solvent for measurement: Deuterated DMSO, Reference material:Trichlorofluoromethane); δ=−113.97 (t, J=15.3 Hz, 2F; CF₂).

EXAMPLE 9-1 [Production of sodium 2-hydroxy-1,1-difluoroethanesulfonate](a 5′th Step: a Saponification Step)

A 2 L reactor was charged with 180.0 g (57% purity, 0.38 mole) of sodium1,1-difluoro-2-(pivaloyloxy)ethanesulfonate obtained by the same methodas that in Example 4-3, 500 mL of water and 95.8 g (1.15 moles/3equivalents) of 48% sodium hydroxide aqueous solution, followed bystirring at room temperature for 1.5 hours. There, 151.0 g (1.53 moles/4equivalents) of 37% hydrochloric acid aqueous solution was added,followed by stirring at room temperature for 1 hour and rinsing twotimes with 250 mL of diisopropyl ether. Then, a solvent was distilledout of the obtained water layer, thereby obtaining 183.7 g of the targetsodium 2-hydroxy-1,1-difluoroethanesulfonate. In this case, purity was38%, and yield was 99%.

Properties of sodium 2-hydroxy-1,1-difluoroethanesulfonate

¹H NMR (Solvent for measurement: Deuterated DMSO, Reference material:Tetramethylsilane); δ=3.80 (t, J=16.0 Hz, 2H; CH₂).

¹⁹F NMR (Solvent for measurement: Deuterated DMSO, Reference material:Trichlorofluoromethane); δ=−115.34 (t, J=16.0 Hz, 2F; CF₂).

EXAMPLE 9-2 [Production of sodium1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonate] (a 6th Step: anEsterification Step 2)

A 10 L reactor was charged with 562.0 g (39% purity, 1.19 moles) ofsodium 2-hydroxy-1,1-difluoroethanesulfonate, 3 kg of acetonitrile, 40mg of nonflex MBP and 367.0 g (2.38 moles/2.0 equivalents) ofmethacrylic anhydride in this order, followed by putting it into an icedbath. There, 361.0 g (3.57 moles/3.0 equivalents) of triethylamine wasadded dropwise. After the dropping, stirring was conducted at roomtemperature for 5 hours. Thereafter, 1.6 L of water was added and thenacetonitrile was distilled off. The obtained water layer was rinsed twotimes with 0.5 L of isopropyl ether, thereby obtaining 288.0 g of thetarget sodium 1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonate (10 wt% aqueous solution). In this case, yield was 96%.

Properties of sodium 1,1-difluoro-2-(2-methacryloyloxy)-ethane sulfonate

¹H NMR (Solvent for measurement: Deuterated DMSO, Reference material:Tetramethylsilane); δ=5.91 (s, 1H), 5.52 (s, 1H), 4.61 (t, J=16.0 Hz,2H; CH₂), 1.81 (s, 3H).

¹⁹F NMR (Solvent for measurement: Deuterated DMSO, Reference material:Trichlorofluoromethane); δ=−113.68 (t, J=16.0 Hz, 2F; CF₂).

EXAMPLE 9-3 [Production of triphenylsulfonium1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonate] (a 7th Step: anOnium-Salt Exchanging Step 2)

A 5 L reactor was charged with 288.0 g of sodium1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonate (10 wt % aqueoussolution) obtained in Example 9-2, 0.8 kg of chloroform and 40 mg ofnonflex MBP. There, an aqueous solution of triphenylsulfonium chloride[409 g (1.37 moles/1.2 equivalents) of triphenylsulfonium chloride and800 g of water] was added dropwise at room temperature, followed bystirring at room temperature for 1.5 hours. Thereafter it was separatedinto a water layer and a chloroform layer. The obtained chloroform layerwas rinsed one time with 2N HCl and six times with water, followed bydistilling chloroform off. There, 1.1 kg of methyl ethyl ketone and 0.3kg of hexane were added, followed by filtration and preparing a methylethyl ketone/hexane mixture solution. On the other hand, a 5 L reactorcharged with 2 L of hexane was prepared, to which the prepared methylethyl ketone/hexane mixture solution was added dropwise at roomtemperature while stirring. After the dropping, stirring was conductedat room temperature for 1 hour. The precipitated solid was separated byfiltration and then dried, thereby obtaining 562 g of the targettriphenylsulfonium 1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonate.In this case, purity was 98%, and yield was 98%.

Properties of triphenylsulfonium1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonate

¹H NMR (Solvent for measurement: Deuterated DMSO, Reference material:Tetramethylsilane); δ=7.92-7.65 (m, 15H, Ph₃S⁺), 6.19 (s, 1H), 5.57 (s,1H), 4.81 (t, J=16.0 Hz, 2H; CH₂), 1.92 (s, 3H).

¹⁹F NMR (Solvent for measurement: Deuterated DMSO, Reference material:Trichlorofluoromethane); δ=−114.49 (t, J=16.0 Hz, 2F; CF₂).

COMPARATIVE EXAMPLE 1

A 30 ml autoclave formed of stainless steel was charged with 2.35 g(11.6 millimoles) of ethyl 2-bromo-2,2-difluoroacetate, 12 ml ofmethanol and 100 mg of an activated carbon-carrying palladium catalyst(metal-carrying amount: 5%, water content: 46%), followed by causing areaction at 40° C. for 2 hours under 1 MPa of hydrogen pressure. Areaction solution was analyzed by using gas chromatography, by whichthere were detected 32% of ethyl 2-bromo-2,2-difluoroacetate and 66% ofethyl 2,2-difluoroacetate which were remained unreacted. The target2-bromo-2,2-difluoroethanol produced was only a little under 2%.

COMPARATIVE EXAMPLE 2

Under a nitrogen atmosphere, a suspension formed containing 6.0 g (88.5millimoles) of active zinc and 50 ml of tetrahydrofuran was slowly addeddropwise to a solution formed containing 9.0 g (44.3 millimoles) ofethyl 2-bromo-2,2-difluoroacetate and 50 ml of tetrahydrofuran at roomtemperature. Thereafter it was heated at 50° C. for 1 hour and thencooled to 0° C. Subsequently, 1M hydrochloric acid was added thereto,followed by extraction with diisopropyl ether. The obtained organiclayer was rinsed with saturated sodium bicarbonate, saturated brine andwater, followed by drying with magnesium sulfate. The organic layer wasanalyzed by gas chromatography, with which about 90% of ethyl2,2-difluoroacetate was detected as the principal product. The target2-bromo-2,2-difluoroethanol was produced little.

COMPARATIVE EXAMPLE 3

Under a nitrogen atmosphere, 1 g (3.39 millimoles) of ethyl6-bromo-5,5,6,6-tetrafluorohexanoate was dissolved in 10 mL oftetrahydrofuran and 1 mL of methanol and then 129 mg (3.39 millimoles)of sodium borohydride was added thereto, followed by stirring at roomtemperature for 1 hour. A reaction solution was extracted with ethylacetate after the addition of a sulfuric acid aqueous solution, followedby concentrating a solvent. With this, ethyl5,5,6,6-tetrafluorohexanoate was obtained at a yield of 50%. Therecannot be confirmed production of 6-bromo-5,5,6,6-tetrafluorohexan-1-ol.

COMPARATIVE EXAMPLE 4

To a solution formed containing 8.92 g (55.4 millimoles) of2-bromo-2,2-difluoroethanol, 12 g of acetonitrile and 22 g of water,5.43 g (64.6 millimoles) of sodium hydrogencarbonate and 9.69 g (55.6millimoles) of sodium dithionite were added. The solution separated intotwo layers was stirred at 60° C. for 12 hours, followed by cooling toroom temperature. Thereafter, a solvent (an organic and a water layer)was distilled off under a reduced pressure and then dried, therebyobtaining 7.0 g of a white solid. The solid was analyzed by nuclearmagnetic resonance (NMR), in which the content of the target sodium1,1-difluoro-2-hydroxyethanesulfinate was about 8% and the yieldobtained by conversion based thereon was 6%.

COMPARATIVE EXAMPLE 5

A glass flask equipped with a thermometer and a condenser was chargedwith 5 g (21.8 millimoles) of2-bromo-2,2-difluoroethyl(2-methylacrylate), 40 g of acetonitrile and 40g of water, followed by stirring. The flask was further charged with 2.2g (26.2 millimoles) of sodium hydrogencarbonate and 5.7 g (32.7millimoles) of sodium dithionite, followed by stirring for 2 hours at60° C. An organic layer of a reaction solution was analyzed by usingnuclear magnetic resonance (NMR), by which there was not detected thetarget sodium 1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfinate butdetected generally only a by-product formed from decomposed methacrylmoiety.

COMPARATIVE EXAMPLE 6

A glass flask equipped with a thermometer and a condenser was chargedwith 6.13 g (21.8 millimoles) of 5-norbornene-2-carboxylic acid2-bromo-2,2-difluoroethyl ester, 40 g of acetonitrile and 40 g of water,followed by stirring. The flask was further charged with 2.2 g (26.2millimoles) of sodium hydrogencarbonate and 5.7 g (32.7 millimoles) ofsodium dithionite, followed by stirring for 1 hour at 65° C. An organiclayer of a reaction solution was analyzed by using nuclear magneticresonance (NMR), by which there was not detected the target sulfinicacid salt but detected generally only a by-product having such a moietyas to lose a double bond.

COMPARATIVE EXAMPLE 7-1 [Production of triphenylsulfonium2-hydroxy-1,1-difluoroethanesulfonate] (a 6′th Step: an Onium-SaltExchanging Step 2)

A 2 L reactor was charged with 183.7 g (38% purity, 0.38 mole) of sodium2-hydroxy-1,1-difluoroethanesulfonate, 300 mL of water, 450 mL ofchloroform and an aqueous solution of triphenylsulfonium chloride [142.8g (0.49 mole/1.25 equivalents) of triphenylsulfonium chloride and 150 mLof water], followed by stirring at room temperature for 1 hour. Areaction solution was analyzed by using nuclear magnetic resonance(NMR), by which there was found almost half raw material sodium2-hydroxy-1,1-difluoroethanesulfonate remaining. Accordingly, thereactor was further charged with an aqueous solution oftriphenylsulfonium chloride [142.8 g (0.49 mole/1.25 equivalents) oftriphenylsulfonium chloride and 150 mL of water], followed by stirringat room temperature for 0.5 hour (triphenylsulfonium chloride was usedin an amount of 285.7 g (0.96 mole/2.5 equivalents) in total and thereaction time was 1.5 hours in total.). The reaction solution wasanalyzed by using nuclear magnetic resonance (NMR), by which the rawmaterial was detected being consumed. Thereafter, the reaction solutionwas separated. The obtained water layer was extracted three times with100 mL of chloroform while distilling a solvent out of the obtainedorganic layer, thereby obtaining 328.2 g of the targettriphenylsulfonium 2-hydroxy-1,1-difluoroethanesulfonate. In this case,purity was 48% and yield was 97%.

In order to achieve an onium-salt exchange, it is thus required to use amonovalent onium salt represented by Q⁺X⁻ (the formula [7]) in an amountnot less than 2 equivalents.

Properties of triphenylsulfonium 2-hydroxy-1,1-difluoroethanesulfonate

¹H NMR (Solvent for measurement: Deuterated DMSO, Reference material:Tetramethylsilane); δ=7.92-7.65 (m, 15H, Ph₃S⁺), 3.81 (t, J=16.0 Hz, 2H;CH₂).

¹⁹F NMR (Solvent for measurement: Deuterated DMSO, Reference material:Trichlorofluoromethane); δ=−115.47 (t, J=16.0 Hz, 2F; CF₂).

COMPARATIVE EXAMPLE 7-1 [Production of triphenylsulfonium1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonate] (a 7′th Step: anEsterification Step 2)

A 2 L reactor was charged with 300.7 g (48% purity, 0.34 mole) oftriphenylsulfonium 2-hydroxy-1,1-difluoroethanesulfonate, 700 mL ofacetonitrile, 104.8 g (0.68 mole/2 equivalents) of methacrylicanhydride, 8.3 g (0.07 mole/0.2 equivalent) of 4-dimethylaminopyridine,34.4 g (0.34 mole/1 equivalent) of triethylamine and 60 mg (0.18millimoles) of nonflex MBP, followed by stirring at 50° C. for 2 hours.Then, a solvent was distilled off and 500 mL of chloroform was addedthereto, thereby obtaining a chloroform solution. Thereafter, thechloroform solution was distilled off, followed by rinsing with dilutedhydrochloric acid and water. The obtained organic substance was rinsedthree times with 300 mL of diisopropyl ether, followed by adding 60 mg(0.18 millimoles) of nonflex MBP and 300 mL of methyl ethyl ketone. Theremaining diisopropyl ether was distilled off, thereby obtaining 129.5 gof the target triphenylsulfonium1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonate serving as a viscousliquid. This liquid had difficulty in crystallizing, so that a furtherpurification could not be achieved. Accordingly, the liquid was dilutedwith methyl ethyl ketone thereby obtaining 440.5 g of 29.4 wt % methylethyl ketone solution. In this case, purity was 98% and yield was 77%.

Thus, the target substance cannot be crystallized by this process, sothat it is difficult to further improve the purity.

TEST EXAMPLE 1 Photoacid Generation Function of triphenylsulfonium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate

An acetonitrile solution of sodium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate synthesized inExample 8 was prepared to have a concentration of 0.05 mol/L. It was putinto a quartz optical cell having an optical path length of 1 cm,followed by irradiation with a light (290 nm) separated from a xenonlamp to conduct actinometry of acid generation. The amount of acidgenerated was observed by absorption of tetrabromophenol blue at 610 nm.Quantity of light was measured with potassium iron trioxalate todetermine quantum yield. With this, it was 0.21 showing a high acidgeneration function.

TEST EXAMPLE 2 Solubility of triphenylsulfonium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate

1.0 g of sodium 2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonatesynthesized in Example 8 was weighed and added to 100 g of propyleneglycol methyl ether acetate, followed by stirring. With this, it wascompletely dissolved.

APPLICATION EXAMPLE 1

A resist was prepared by dissolving 2 parts by weight oftriphenylsulfonium 1,1-difluoro-2-(valeryloxy)ethanesulfonate mentionedin Example 7, 100 parts by weight of a polymer having a weight averagemolecular weight of 15,000, in which hydroxy groups ofpolyhydroxystyrene have been protected with 15 mol % of 1-ethoxyethylgroup and 15 mol % of tert-butoxycarbonyl group, and 0.2 part by weightof isopropanolamine in 600 parts by weight of propylene glycolmonomethyl ether acetate.

APPLICATION EXAMPLE 2

A resist was prepared by dissolving 2 parts by weight oftriphenylsulfonium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate mentioned inExample 8, 100 parts by weight of a polymer having a weight averagemolecular weight of 15,000, in which hydroxy groups ofpolyhydroxystyrene have been protected with 35 mol % of 1-ethoxyethylgroup, and 0.2 parts by weight of isopropanolamine in 600 parts byweight of propylene glycol monomethyl ether acetate.

APPLICATION EXAMPLE 3

A resist was prepared by dissolving 5 parts by weight oftriphenylsulfonium2-(1′-adamantane)carbonyloxy-1,1-difluoroethanesulfonate mentioned inExample 8, 100 parts by weight of a terpolymer (weight average molecularweight 12800) of 45 mol % methyladamantanemethacrylate/25 mol %hydroxyadamantanemethacrylate/30 mol γ-butyrolactonemethacrylate, and0.1 parts by weight of triethanolamine in 800 parts by weight ofpropylene glycol monomethyl ether acetate.

TEST EXAMPLE 3

The resists of Application Examples 1, 2 and 3 were filtered by amembrane filter of 0.2 μm to prepare radiosensitive resin compositionsolutions. Then, the composition solutions were applied on siliconwafers with a rotation speed of 1500 rpm. Then, they were dried at 100°C. for 90 seconds on a hot plate to form resist films having a filmthickness of 320 nm. The obtained films were homogeneous and good.

This resist film was subjected to exposure by using an ultraviolet rayby a high-pressure mercury light. After exposure, heating was conductedon the hot plate at 110° C. for 90 seconds. An immersion phenomenon wasconducted for 60 seconds in 2.38% tetramethylammonium hydroxide aqueoussolution, and rinse was conducted for 30 seconds with pure water.

As a result, in all of Application Examples 1, 2 and 3 there wereobtained rectangular, positive-type, good patterns having less edgeroughness.

Regarding sulfonium salts (PAG 1 and 2) represented by the followingformulas, there were conducted evaluations of compatibility andresolution when resists were formed.

TEST EXAMPLES 4 TO 11

Evaluations of PAG Compatibility and Resist Resolution

A resist material was prepared by using a sulfonium salt (PAG 1 or 2)represented by the above formula as an acid generator and a polymer(resin 1-4) represented by the following formula as a base resin.Furthermore, each composition was filtered by a membrane filter of 0.2μm to prepare each resist solution.

Then, all of the resist solutions were applied on silicon wafers by spincoating to obtain resist films having a film thickness of 250 nm. Afterconducting a prebaking at 110° C., exposure was conducted with 248 nmultraviolet ray through a photomask, and then a post-exposure baking wasconducted at 120° C. After that, development was conducted at 23° C. for1 minute by using 2.38 wt % tetramethylammonium hydroxide aqueoussolution. Composition and evaluation results of each resist are shown inTable 1.

TABLE 1 Acid Resin Generator Solvent Test (parts by (parts by (parts byCompat- Pattern Example wt.) wt.) wt.) ibility Shape 4 Resin 1 PAG1PGMEA Good Clean (40) (1.0) (400) rectangular 5 Resin 1 PAG2 PGMEA GoodClean (40) (1.0) (400) rectangular 6 Resin 2 PAG1 PGMEA Good Clean (40)(1.0) (400) rectangular 7 Resin 2 PAG2 PGMEA Good Clean (40) (1.0) (400)rectangular 8 Resin 3 PAG1 PGMEA Good Clean (40) (1.0) (400) rectangular9 Resin 3 PAG2 PGMEA Good Clean (40) (1.0) (400) rectangular 10 Resin 4PAG1 PGMEA Good Clean (40) (1.0) (400) rectangular 11 Resin 4 PAG2 PGMEAGood Clean (40) (1.0) (400) rectangular

COMPARATIVE EXAMPLES 8 TO 15

For comparison, with respect to sulfonium salts (PAG 3 and 4)represented by the following formulas, evaluations of compatibility ofPAG when made into resists and resolution of resists are shown in Table2.

[Chemical Formula 76]

TABLE 2 Acid Compar- Resin Generator Solvent ative (parts by (parts by(parts by Compat- Pattern Example wt.) wt.) wt.) ibility Shape 8 Resin 1PAG 3 PGMEA Good Somewhat (40) (1.0) (400) head-swollen shape 9 Resin 1PAG 4 PGMEA Good Somewhat (40) (1.0) (400) distorted rectangular 10Resin 2 PAG 3 PGMEA Somewhat Somewhat (40) (1.0) (400) defectivehead-swollen shape 11 Resin 2 PAG 4 PGMEA Good Clean (40) (1.0) (400)rectangular (inferior to Test Example 7) 12 Resin 3 PAG 3 PGMEA SomewhatSomewhat (40) (1.0) (400) defective head-swollen shape 13 Resin 3 PAG 4PGMEA Good Clean (40) (1.0) (400) rectangular (inferior to Test Example9) 14 Resin 4 PAG 3 PGMEA Somewhat Somewhat (40) (1.0) (400) defectivehead-swollen shape 15 Resin 4 PAG 4 PGMEA Good Somewhat (40) (1.0) (400)distorted rectangular (inferior to Test Example 11)

From the results of Table 1 and Table 2, it was confirmed that the acidgenerators of the present invention had resolutions higher than those ofconventional products.

1. Triphenylsulfonium1,1-difluoro-2-(2-methacryloyloxy)-ethanesulfonate.